home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
DP Tool Club 8
/
CDASC08.ISO
/
VRAC
/
TREPLN21.ZIP
/
TREEPLAN.DOC
< prev
next >
Wrap
Text File
|
1993-08-12
|
263KB
|
6,034 lines
TreePlan for DOS
Decision Tree Software
Version 2.1
+----------
|
/
+----------()------------
| \
/ |
[] +----------
\
|
+----------
Program and User's Manual
by
Michael R. Middleton
University of San Francisco
Copyright 1993
Michael R. Middleton
All Rights Reserved
Published
by
Decision Support Services
2105 Buchanan Street, #1
San Francisco, CA 94115
Voice/Fax (415) 673-6217
Compuserve 71330,3445
TreePlan User's Manual Page i
Warranty
------------------------------------------------------------------
Users of TreePlan must accept this disclaimer of warranty:
TreePlan copyrighted software and documentation are provided on an
'as is' basis. The author and Decision Support Services disclaim
all warranties, expressed or implied, including, without
limitation, the warranties of merchantability and of fitness for
any purpose. The user assumes all risks as to the quality and
performance of this software and documentation. The author and
Decision Support Services assume no liability for indirect,
consequential, or incidental damages which may result from the use
or misuse of TreePlan. Some states do not allow the exclusion of
the limit of liability for consequential or incidental damages, so
the above limitation may not apply to you. This agreement shall
be governed by the laws of the State of California and shall inure
to the benefit of the author and Decision Support Services and any
successors, administrators, heirs, and assigns. Any action or
proceeding brought by either party against the other arising out
of or related to this agreement shall be brought only in a state
or federal court of competent jurisdiction located in the city and
county of San Francisco, California. The parties hereby consent
to in personam jurisdiction of said courts.
Shareware
------------------------------------------------------------------
Shareware is a method of distributing software that gives you a
chance to try software before buying it. If you try a shareware
program and continue using it, you are expected to register.
Individual programs differ on the details about the evaluation
period, registration fee, and support.
Copyright laws apply to both shareware and commercial software,
and the copyright holder may choose to retain all rights. The
only meaningful difference between shareware and commercial
software is the method of distribution. Shareware authors
specifically grant the rights to copy and distribute the software
and documentation, either to all users and by all methods, or with
some restrictions.
You should try to find software that suits your needs and budget,
whether it's commercial or shareware. Both types have good
programs and bad, but shareware makes finding the right program
easier, because you can try before you buy. Also, because
shareware distribution costs are much lower, shareware prices are
often lower, too. Finally, shareware has the ultimate money-back
guarantee: if you don't use it, you don't pay for it.
TreePlan User's Manual Page ii
Registration
------------------------------------------------------------------
TreePlan is a shareware product and may be provided at no charge
to the user for evaluation. If you find this program useful and
continue to use TreePlan after a 90-day evaluation period, you
must make a registration payment to Decision Support Services.
The registration fee will license one copy for use on any one
computer at any one time.
To register TreePlan by cash, check, or money order, please print
the ORDER.DOC text file and mail directly to Decision Support
Services. The registration fee is $29.00 (California residents,
add sales tax) plus $4.00 shipping to U.S. and Canada, $6.00
elsewhere. Make money order or check (in U.S. funds drawn on a
U.S. bank) payable to Decision Support Services, and mail to
Decision Support Services, 2105 Buchanan Street, #1, San
Francisco, CA 94115.
For credit card orders, please see the VISA&MC.DOC text file.
Upon registering TreePlan, you will be sent by postal mail a
formatted, laser-printed, bound copy of the User's Manual and
disks containing the most recent version of the software and
documentation. Registered users will be notified of the next
major version and are entitled to 90 days of technical support
via postal mail, phone, fax, or Compuserve 71330,3445.
A site license agreement is required to use TreePlan on a computer
network or to permit copying of the documentation for users within
an organization. Technical support is provided only to one
representative of the organization. The User's Manual may not be
copied unless a site license agreement has been signed. Please
see the SITELICE.DOC text file for additional information and an
order form.
Distribution
------------------------------------------------------------------
Please share copies of the TreePlan disks freely with prospective
users. You are granted permission to make as many copies as you
wish. Do not alter the program, data files, or documentation.
Please see the LICENSE.DOC text file for additional information.
Be sure to include the complete TreePlan package, including
program, sample decision tree data files, documentation on disk,
TreePlan User's Manual Page iii
and all other files listed in the PACKING.LST text file. If any
files listed in PACKING.LST, or the PACKING.LST file itself, are
missing, then the package is not complete and distribution is
forbidden. Please contact Decision Support Services to obtain a
complete package suitable for distribution.
Disk vendors, bulletin boards, other distributors, and individuals
may distribute the complete TreePlan package for a distribution
fee not exceeding $12 as long as you clearly explain the shareware
concept, the need for users to register the products they use, and
the fact that the price of your disks/service is a copying fee
only and does not constitute payment for the product. Please see
the VENDOR.DOC, SYSOP.DOC, and DESCRIBE.DOC text files for
additional information.
ASP Ombudsman
------------------------------------------------------------------
This program is produced by a member of the Association of
Shareware Professionals (ASP). ASP wants to make sure that the
shareware principle works for you. If you are unable to resolve
a shareware-related problem with an ASP member by contacting the
member directly, ASP may be able to help. The ASP Ombudsman can
help you resolve a dispute or problem with an ASP member, but
does not provide technical support for members' products. Please
write to the ASP Ombudsman at 545 Grover Road, Muskegon, MI
49442-9427 or send a Compuserve message via Compuserve Mail to
ASP Ombudsman 70007,3536.
TreePlan User's Manual Page iv
Table of Contents
Chapter 1: Introduction 1
What TreePlan Can Do 1
Necessary Equipment 2
Optional Equipment 2
Installing TreePlan 2
Files on disk 3
Floppy-drive installation 3
Hard-drive installation 4
Reading the README.DOC file 4
Starting and stopping TreePlan 5
Chapter 2: Basic Decision Tree Concepts 7
DriveTek Problem 7
Nodes and Branches 8
Terminal Values 9
DriveTek Unsolved Tree 10
Strategy 11
Payoff Distribution 12
Certainty Equivalent 12
DriveTek Strategies 13
Rollback Method 16
DriveTek Solved Tree 17
Sensitivity Analysis 18
Probability 18
Value 20
Chapter 3: Advanced Decision Tree Concepts 21
Risk Attitude 21
Sensitivity Analysis 27
Lottery Certainty Equivalent 27
Risk Coefficient 29
Expected Value of Perfect Information 30
Valley Problem (A) 30
Valley EVPI Tree 31
Bayesian Revision of Probabilities 34
Valley Problem (B) 38
Valley Solved Tree 43
Expected Value of Sample Information 44
Valley EVSI Tree 46
Risk Attitude and Value of Information 47
TreePlan User's Manual Page v
Chapter 4: General Treeplan Features 49
Screen Layout 49
TreePlan Modes 51
Tree Navigation In READY Mode 52
Chapter 5: Building A Tree With TreePlan 55
Step 1: Node Add Option 56
Step 2: Node Event Option 56
Step 3: Node Decision Option 57
Step 4: Node Event Option 58
Step 5: Node Decision Option 59
Step 6: Node Copy Option 59
Chapter 6: TreePlan Menu Options 61
Node Menu Options 61
Node Decision Option 62
Node Event Option 62
Node Add Option 62
Node Copy Option 63
Node Insert Option 63
Node Oops Option 64
Node Shorten Option 64
Node Terminal Option 64
Node Remove Option 65
Node New Option 65
Solve Menu Options 65
Solve Risk Options 66
Solve Risk Change Options 66
Solve Risk Max/Min Option 67
Solve Risk Neutral Option 67
Solve Risk Direct Option 67
Solve View Option 68
Solve Distribution Options 68
Solve Distribution Screen Option 68
Solve Distribution Printer/File Options 69
Solve Print Options 69
Solve Print Screen Option 69
Solve Print Printer/File Options 70
TreePlan User's Manual Page vi
Print Menu Options 70
Print Screen Option
Print Printer/File Options 71
File Menu Options 71
File Retrieve Option 72
File Save Option 72
File Erase Tree/Print Options 73
File List Tree/Print Options 73
File Directory Option 73
EVPI Menu Options 73
EVPI View Option 74
EVPI Retain Option 75
Bayes Menu Options 75
Bayes Link Options 75
Bayes Input Options 76
Bayes Screen Option 77
Bayes Printer/File Options 77
Bayes Transfer Options 78
Table Value Menu Options 78
Table Value Load Option 78
Table Value View Option 79
Table Value Printer/File Options 79
Table Probability Menu Options 80
Table Probability Load Option 80
Table Probability Tenths Option 81
Table Probability View Option 81
Table Probability Printer/File Options 81
Table Lottery-CE Menu Options 81
Table Lottery-CE Load Option 82
Table Lottery-CE View Option 82
Table Lottery-CE Printer/File Options 83
Table Risk-Coefficient Menu Options 83
Table Risk-Coefficient Load Option 83
Table Risk-Coefficient View Option 84
Table Risk-Coefficient Printer/File Options 84
TreePlan User's Manual Page vii
Default Menu Options 84
Default Format Options 85
Default Layout Options 86
Default Setup Option 87
Default Printer Options 87
Default Directory Option 88
Default Clear Option 88
Default Update Option 89
Zoom Menu Options 89
Zoom Screen Option 89
Zoom Printer/File Options 90
Appendix A: References 91
Appendix B: TreePlan Error Messages 92
Index 96
TreePlan User's Manual Page viii
Chapter 1: Introduction
******************************************************************
This chapter discusses TreePlan's features, the computer equipment
supported by TreePlan, and the installation procedures for
preparing TreePlan to run on your system.
What TreePlan Can Do
==================================================================
TreePlan is a computer program for analyzing decision tree models.
Decision trees are especially appropriate for analyzing sequential
decision problems under uncertainty. For information about
decision tree concepts, basic and advanced, please see Chapter 2
and Chapter 3.
TreePlan decision tree software includes the following features:
Create and modify decision tree models on screen
Save and retrieve tree data files
Print the decision tree diagram, unsolved or solved
Solve (rollback) using expected value or a utility function
Assess risk attitude using an exponential utility function
Automatically compute Expected Value of Perfect Information
Revise prior probabilities using Bayes rule
Perform sensitivity analysis of cash flows, probabilities, or
risk attitude
Use horizontal-bar menus to choose commands
Select extensive on-screen help
For information about TreePlan's general features and menu
options, please see Chapter 4 and Chapter 6.
Chapter 1: Introduction Page 1
Necessary Equipment
==================================================================
You need the following equipment to run TreePlan:
Computer: TreePlan is designed to run on the IBM PC, XT, AT,
PS/2, and fully compatible personal computers.
Operating System: TreePlan runs on DOS 2.0 or later (either PC-
DOS or MS-DOS).
Memory: To run TreePlan, your computer must have a minimum of
approximately 384 kilobytes (384 KB) of random access memory
(RAM).
Disk Drive: TreePlan will run on a minimal system with only a
single floppy drive (double-sided 5.25-inch 360 KB).
TreePlan also runs on higher density floppy drives (720 KB,
1.2 MB, and 1.44 MB), hard drives, and electronic disks
(virtual or RAM disks).
Optional Equipment
==================================================================
The following equipment is not required to run TreePlan:
Printer: You can use a dot matrix, daisy wheel, or laser printer
for printing TreePlan's diagrams and tables. The printer
interface can be either parallel or serial. PostScript
printers are not directly supported.
Graphics card: You can run TreePlan on a system with a text-only
monochrome adapter card or a graphics card. The monochrome
or color monitor attached to the card must support an 80-
column display. TreePlan automatically detects the type of
graphics card you're using and acts accordingly.
TreePlan does not make use of expanded or extended memory, a
mouse, or a math coprocessor.
Installing TreePlan
==================================================================
The following sections discuss the files on the original TreePlan
TreePlan User's Manual Page 2
disk (or disks), installation procedures for floppy-drive and
hard-drive systems, and methods for reading the README.DOC file.
Files on disk
------------------------------------------------------------------
The original TreePlan disk includes the following files:
TREEPLAN.EXE TreePlan program
DRIVETEK.TRE sample tree data file
VALLEY_A.TRE sample tree data file
VALLEY_B.TRE sample tree data file
README.DOC late-breaking news, if any
The following file may be on the same disk (3.5-inch) or on a
separate disk (5.25-inch):
TREEPLAN.DOC documentation (this User's Manual)
Put a write-protect tab on the original TreePlan 5.25-inch disk
(or open the write-protect window in the upper right-hand corner
of the 3.5-inch disk) before you copy the files to your hard disk
or floppy work disk. Then store the original in a safe place free
of dirt, moisture, and magnetic fields.
Floppy-drive installation
------------------------------------------------------------------
If you're using a floppy-drive system with no hard disk (or if you
always want to run TreePlan from a floppy drive), you should make
a work disk before using TreePlan.
Most floppy-drive computers have one floppy-drive named A and a
second floppy-drive named B. If your floppy-drives are named
differently, make the appropriate substitutions as you read the
instructions below.
(1) Be sure the original TreePlan disk is write-protected.
(2) Place the original TreePlan disk in drive A and a blank,
formatted disk in drive B. (Refer to your DOS manual for
instructions for formatting a disk.)
(3) Type COPY A:*.* B: and press Enter. This command tells DOS
to copy all files on drive A to drive B.
Chapter 1: Introduction Page 3
(4) After all files are copied, remove the original TreePlan disk
from drive A and store it safely. Affix a label to the disk
in drive B to identify it as your TreePlan work disk.
Hard-drive installation
------------------------------------------------------------------
If you have a hard-disk system, you probably want to copy the
TreePlan files into a directory on the hard disk. In the
following procedure, you first create a directory called TREEPLAN
off the root directory and then copy your TreePlan files into it.
Most hard disk computers have a floppy disk drive named A and a
hard disk drive named C. If your drives are named differently,
make the appropriate substitutions as you read the instructions
below.
(1) At the DOS prompt, type C: and press Enter to make drive C
the current drive.
(2) Type CD C:\ and press Enter to go to the root directory.
(3) Make a new directory called TreePlan. Type MD TREEPLAN and
press Enter.
(4) Change to the new directory. Type CD TREEPLAN and press
Enter.
(5) Be sure the original TreePlan disk is write-protected.
Insert it in floppy drive A and type COPY A:*.* C: and press
Enter.
(6) After all files are copied, remove the TreePlan disk from
drive A and store it safely.
It is usually convenient to keep your tree data files in the same
directory as the TreePlan program files, but you can put them in a
separate directory if you wish.
Reading the README.DOC file
------------------------------------------------------------------
Any last-minute changes or additions to the TreePlan program are
documented in a file called README.DOC. You should review this
file carefully before working with TreePlan and make note of any
TreePlan User's Manual Page 4
changes.
To display the README.DOC file, go to the directory containing
your TreePlan files. At the DOS prompt, type TYPE README.DOC and
press Enter to view the file.
You can send the README.DOC file to your printer using one of the
following DOS commands.
PRINT README.DOC
COPY README.DOC PRN
TYPE README.DOC > PRN
Starting and stopping TreePlan
==================================================================
If you are using TreePlan on a floppy disk, insert the TreePlan
work disk in floppy drive A. At the DOS prompt, type A: and press
Enter to make drive A the default drive. To start TreePlan, type
TREEPLAN and press Enter.
If you using TreePlan on a hard-disk system, move to the directory
containing the TreePlan program files. For example, if the
program files are in directory TREEPLAN on drive C, at the DOS
prompt, first type C: and press Enter to make drive C the default
drive, and then type CD TREEPLAN and press Enter to move to the
TreePlan directory. To start TreePlan, type TREEPLAN and press
Enter.
You can also start TreePlan using one or both of the two command-
line switches. If you want TreePlan to display a larger cursor
that is easier to see (e.g., if you're using a laptop computer),
type TreePlan B at the DOS prompt and press Enter. If you're
using a somewhat non-standard video display, you may want to
override TreePlan's autodetection of your graphics card and force
TreePlan to use monochrome "colors"; at the DOS prompt, type
TreePlan M and press Enter. If you want both a block cursor and
monochrome, type TreePlan BM and press Enter.
To stop TreePlan, first press the Escape key repeatedly until the
mode indicator in the upper-right corner of the screen shows
READY. In READY mode, type /Q to quit using the program. (If you
have made changes to your decision tree since you last saved the
tree data on disk, you will be asked to confirm that you want to
quit without saving.)
While selecting menu options or editing an entry, you can always
use the Escape key to cancel an operation or back out of a
Chapter 1: Introduction Page 5
situation. If you press the Escape key repeatedly, you will
always return to READY mode.
TreePlan User's Manual Page 6
Chapter 2: Basic Decision Tree Concepts
******************************************************************
This chapter reviews some basic concepts concerning decision tree
models, including nodes, branches, terminal values, strategy,
payoff distribution, certainty equivalent, and the rollback
method.
It is especially important to understand the concept of a strategy
before using TreePlan. If you are familiar with decision tree
terminology and concepts, you may want to skim this chapter and
Chapter 3 quickly; then refer to Chapter 4 for TreePlan's general
features. If you are not well-acquainted with decision trees, you
should study this chapter and Chapter 3 carefully and also consult
other references.
Decision trees are useful models for analyzing sequential decision
problems under uncertainty. A decision tree is a graphic model
which describes the decisions to be made, the events that may
occur, and the outcomes associated with combinations of decisions
and events. Probabilities are assigned to the events, and values
are determined for each outcome. A major goal of the analysis is
to determine the best strategy.
The following problem, adapted from an example in the Spurr text
(1973), will be used to illustrate the basic concepts of decision
tree modeling.
DriveTek Problem
==================================================================
The management of DriveTek Research Institute has learned that
Artex Computers is interested in developing a tape drive for a
proposed new computer system. Artex does not have research people
available to develop the new drive itself, so the company is going
to subcontract the development to an independent research firm.
Artex has offered a fee of $250,000 for developing the new tape
drive and has asked for proposals from various research firms.
The contract is to be awarded not on the basis of price (set at
$250,000) but on the basis of both the technical plan shown in the
proposal and the reputed technical competence of the firm
submitting the proposal.
DriveTek Research Institute is considering submitting a proposal
to Artex Computer to develop the new tape drive. DriveTek
Research management estimates that it will cost about $50,000 to
prepare a proposal; further, they estimate that the chances are
Chapter 2: Basic Decision Tree Concepts Page 7
about 50/50 that they will be awarded the contract.
However, DriveTek Research engineers are uncertain about how they
will develop the tape drive if they are awarded the contract.
Three alternative approaches can be tried. The first approach is
a mechanical method with a cost of $120,000, and the engineers are
certain they can develop a successful model with this approach. A
second approach involves the use of electronic components. The
engineers estimate that it will cost only $50,000 to develop a
model of the tape drive using the electronic approach, but that
there is only a 50 percent chance that the results will be
satisfactory. A third approach involves the use of magnetic
components; the cost of developing a model using this approach
will be $80,000, with a 70 percent chance of success.
DriveTek Research has sufficient time to try only two approaches.
Thus, if they try either the magnetic or electronic method and it
fails, the second attempt will have to use the mechanical method
in order to guarantee a successful model.
The management of DriveTek Research is uncertain about how to take
all this information into account in making the immediate decision
about whether to spend $50,000 to develop a proposal to send to
Artex Computers.
Nodes and Branches
==================================================================
TreePlan uses three kinds of nodes and two kinds of branches to
represent a decision tree. A decision node is a point where a
choice must be made, usually shown as a square on hand-drawn
decision trees. TreePlan shows a decision node as square
brackets, [], sometimes with the letter D between the square
brackets to emphasize that it is a decision node, [D]. The
branches extending from a decision node are decision branches,
each branch representing one of the possible alternatives or
courses of action that are available at that point.
There are two major decisions in the DriveTek problem. First,
they must decide whether to prepare a proposal or not. Second, if
they prepare a proposal and are awarded the contract, they must
decide which of the three approaches to use to satisfy the
contract.
An event node is a point where uncertainty is resolved, i.e., a
point where the decision maker learns about the occurrence of an
event. An event node, sometimes called a "chance node," is
usually shown as a circle on decision diagrams. TreePlan shows an
TreePlan User's Manual Page 8
event node as curved parentheses, (), sometimes with the letter E
between the parentheses to emphasize that it is an event node,
(E). The event set consists of the event branches extending from
an event node, each branch representing one of the possible events
that may occur at that point.
There are three sources of uncertainty in the DriveTek problem:
whether they are awarded the contract or not, whether the
electronic approach is OK or bad, and whether the magnetic
approach is OK or bad.
In general, decision nodes and branches represent the controllable
factors in a decision problem; event nodes and branches represent
uncontrollable factors.
The third kind of node is a terminal node, representing the final
result of a combination of decisions and events. Terminal nodes
are the endpoints of a decision tree. TreePlan shows a terminal
node as a pair of vertical lines, ||, sometimes with the letter T
between the lines to emphasize that it is a terminal node, |T|.
The following table summarizes the three kinds of nodes and two
kinds of branches that TreePlan uses to represent a decision tree.
Type of Written TreePlan
Node Symbol Symbol Node Successor
-------- -------- --------- --------------
Decision square [] or [D] decision branches
Event circle () or (E) event branches
Terminal endpoint || or |T| terminal value
Terminal Values
==================================================================
Each terminal node has an associated terminal value, sometimes
called a payoff value, outcome value, or endpoint value. Each
terminal value measures the result of a scenario, i.e., the
sequence of decisions and events on a unique path leading from the
initial decision node to a specific terminal node.
TreePlan lets you assign a partial-cash-flow value to each
decision branch and event branch, and TreePlan automatically sums
the partial-cash-flow values on the branches leading to a terminal
node to determine the terminal value.
If you want to assign terminal values directly instead of using
partial-cash-flows, simply assign zero value to all branches
except the branches immediately preceding the terminal nodes.
Chapter 2: Basic Decision Tree Concepts Page 9
On an unsolved tree, the branch name, probability, and partial-
cash-flow value are arranged as follows.
Branch name
Decision branch: [D]------------------------...
Value
Branch name
Event branch: (E)------------------------...
Value Probability
In the DriveTek problem, there are distinct partial-cash-flows
associated with many of the decision and event branches. In other
decision problems under uncertainty, it may be necessary to use a
more elaborate financial model to determine the terminal values.
DriveTek Unsolved Tree
==================================================================
A condensed version of the unsolved decision tree model for the
DriveTek problem is shown below. Partial-cash-flows and terminal
values are in thousands of dollars. (The diagram was prepared
using TreePlan, printed to a file, and condensed with a word
processor so that it would fit on a single page.)
TreePlan User's Manual Page 10
Use mech
+----------||........................ +80
| -120
|
| Elec OK
| +----------||............+150
| Try elec | 0 0.5
Awarded +----------()
+----------[] -50 | Elec bad Use mech
| +250 0.5 | +----------[]----------|| +30
| | 0 0.5 -120
| |
| | Mag OK
Prepare | | +----------||............+120
+----------() | Try mag | 0 0.7
| -50 | +----------()
| | -80 | Mag bad Use mech
| | +----------[]----------|| 0
| | 0 0.3 -120
[] |
| | No award
| +----------||.................................... -50
| 0 0.5
|
| Don't
+----------||................................................ 0
0
For example, the +30 (thousand dollars) terminal value on the far
right of the diagram is associated with the following scenario:
Branch type Branch name Partial-cash-flow
----------- ----------- -----------------
Decision Prepare proposal -50
Event Awarded contract +250
Decision Try electronic approach -50
Event Electronic approach bad 0
Decision Use mechanical approach -120
----
Terminal value +30
Strategy
==================================================================
A strategy is a specification of an initial choice and any
subsequent choices to be made by the decision maker. The
subsequent choices are usually conditional on events. The
Chapter 2: Basic Decision Tree Concepts Page 11
specification of a strategy must be comprehensive; if the
decision maker gives the strategy to a colleague, the colleague
must know exactly which choice to make at each decision node that
might be encountered.
Most decision problems have many possible strategies, and a goal
of the analysis is to determine the optimal strategy, taking into
account the decision maker's risk attitude.
There are four strategies in the DriveTek problem. For example,
one of the strategies could be stated as follows: Prepare the
proposal; if not awarded the contract, stop; if awarded the
contract, try the magnetic method; if the magnetic method is OK,
stop; if the magnetic method is bad, use the mechanical method.
The four strategies will be discussed in detail below.
Payoff Distribution
==================================================================
Each strategy has an associated payoff distribution, sometimes
called a risk profile. The payoff distribution of a particular
strategy is a probability distribution showing the probability of
obtaining each terminal value associated with a particular
strategy.
In decision tree models, the payoff distribution can be shown as a
list of possible payoff values, x, and the discrete probability of
obtaining each value, P(X=x), where X represents the uncertain
terminal value. Since each strategy can be characterized by its
payoff distribution, the goal of selecting the best strategy
becomes a problem of choosing the best payoff distribution. One
approach for making the choice is to use certainty equivalents,
described in the next section.
Certainty Equivalent
==================================================================
A certainty equivalent is a certain payoff value which is
equivalent, for the decision maker, to a particular payoff
distribution. If the decision maker can determine his or her
certainty equivalent for the payoff distribution of each strategy,
then the optimal strategy is the one with the highest certainty
equivalent.
The certainty equivalent, i.e., the minimum selling price for a
payoff distribution, depends on the decision maker's personal
TreePlan User's Manual Page 12
attitude toward risk. A decision maker may be risk preferring,
risk neutral, or risk avoiding. For additional information,
please consult the Risk Attitude section of Chapter 3.
If the terminal values are not regarded as extreme (relative to
the decision maker's total assets), if the decision maker will
encounter other decision problems with similar payoffs, and if the
decision maker has the attitude that he or she will "win some and
lose some," then the decision maker's attitude toward risk may be
described as risk neutral.
If the decision maker is risk neutral, the certainty equivalent of
a payoff distribution is equal to its expected value. The
expected value of a payoff distribution is calculated by
multiplying each terminal value by its probability and summing the
products.
The next section illustrates each of the four strategies of the
DriveTek problem.
DriveTek Strategies
==================================================================
Each strategy is described by a shorthand statement and a more
detailed statement. The branches that might be encountered when
the decision maker follows the strategy are shown in decision tree
form; the appropriate branches are extracted from the unsolved
tree diagram without showing partial-cash-flow values.
Each payoff distribution is shown as a discrete probability
distribution, with value x and probability P(X=x). Since a
strategy specifies a choice at each decision node, the uncertainty
about terminal values depends only on the occurrence of events.
The probability of obtaining a terminal value is calculated as the
joint probability of the events on the path leading to the
terminal node.
If the decision maker is risk neutral, the expected value is the
appropriate certainty equivalent for choosing among the
strategies.
Strategy 1: Prepare; if Awarded, Use mech.
Details: Prepare the proposal; if not awarded the contract, stop
(payoff = -50); if awarded the contract, use the mechanical
method (payoff = +80).
Chapter 2: Basic Decision Tree Concepts Page 13
Use mech
+----------||........................ +80
|
Awarded |
+----------[]
| 0.5
Prepare |
+----------()
| |
[] | No award
+----------||.................................... -50
0.5
Value Prob.
----- -----
+80 .50
-50 .50
----- ----- (Expected Value = +15)
1.00
Strategy 2: Prepare; if Awarded, Try elec.
Details: Prepare the proposal; if not awarded the contract, stop
(payoff = -50); if awarded the contract, try the electronic
method; if the electronic method is OK, stop (payoff = +150); if
the electronic method is bad, use the mechanical method (payoff =
+30).
Elec OK
+----------||............+150
Try elec | 0.5
Awarded +----------()
+----------[] | Elec bad Use mech
| 0.5 +----------[]----------|| +30
Prepare | 0.5
+----------()
| |
[] | No award
+----------||.................................... -50
0.5
TreePlan User's Manual Page 14
Value Prob.
----- -----
+150 .25
+30 .25
-50 .50
----- ----- (Expected Value = +20)
1.00
Strategy 3: Prepare; if Awarded, Try mag.
Details: Prepare the proposal; if not awarded the contract, stop
(payoff = -50); if awarded the contract, try the magnetic method;
if the magnetic method is OK, stop (payoff = +120); if the
magnetic method is bad, use the mechanical method (payoff = 0).
Awarded
+----------[]
| 0.5 |
| | Mag OK
Prepare | | +----------||............+120
+----------() | Try mag | 0.7
| | +----------()
| | | Mag bad Use mech
| | +----------[]----------|| 0
| | 0.3
[] |
| No award
+----------||.................................... -50
0.5
Value Prob.
----- -----
+120 .35
0 .15
-50 .50
----- ----- (Expected Value = +17)
1.00
Strategy 4: Don't.
Details: Don't prepare the proposal (payoff = 0).
Chapter 2: Basic Decision Tree Concepts Page 15
[]
|
| Don't
+----------||................................................ 0
Value Prob.
----- ----- (Expected Value = 0)
0 1.00
Rollback Method
==================================================================
If you examine the four strategies in the previous section, you
will see that strategy 2 has the payoff distribution with the
highest expected value. If we have a method for determining
certainty equivalents, e.g., expected values for a risk neutral
decision maker, we don't need to examine every possible strategy
explicitly. Instead, we can use the rollback method to determine
the single best strategy.
The rollback algorithm, sometimes called backward induction,
starts at the terminal nodes of the tree and works backward to the
initial decision node, determining the certainty equivalent for
each node. At each event node, the certainty equivalent is
determined using expected value if the decision maker is risk
neutral; at each decision node, the certainty equivalent is set
equal to the highest certainty equivalent on the immediate
successor nodes.
When the rollback method has finished assigning certainty
equivalents to each node, we can work forward through the tree to
identify the optimal strategy. TreePlan uses double lines instead
of single lines to indicate branches that are part of the optimal
strategy. For standard printers without the line-drawing
characters, TreePlan uses equal signs for branches of the optimal
strategy, =====, and dashes for other branches, -----.
Partial-cash-flow values are not shown on a solved tree; the
branch name, probability, and rollback certainty equivalent (CE)
of the successor node are arranged as follows.
TreePlan User's Manual Page 16
Rollback CE
Decision branch: [D]========================...
Branch name
Prob. Rollback CE
Event branch: (E)========================...
Branch name
DriveTek Solved Tree
==================================================================
A condensed version of the solved decision tree for the DriveTek
problem is shown below.
+80
+----------||........................ +80
| Use mech
|
| 0.5 +150
| +==========||............+150
| +90 | Elec OK
0.5 +90 +==========()
+==========[] Try elec | 0.5 +30 +30
| Awarded | +==========[]==========|| +30
| | Elec bad Use mech
| |
| | 0.7 +120
+20 | | +----------||............+120
+==========() | +84 | Mag OK
| Prepare | +----------()
| | Try mag | 0.3 0 0
| | +----------[]----------|| 0
| | Mag bad Use mech
[] |
| | 0.5 -50
| +==========||.................................... -50
| No award
|
| 0
+----------||................................................ 0
Don't
The rollback method has identified strategy 2 as being optimal,
and the rollback value on the initial branch of the optimal
strategy is +20, the same as the expected value for the payoff
distribution of strategy 2.
Chapter 2: Basic Decision Tree Concepts Page 17
Sensitivity Analysis
==================================================================
A decision maker may not be completely confident about his or her
preliminary probability assignments and partial-cash-flow
estimates. Sensitivity analysis can be used to determine whether
or not the optimal strategy is sensitive to changes in the base-
case probabilities and values. If a small change in one of the
inputs indicates that a different strategy is optimal, then the
decision maker should think very carefully about that probability
or value before implementing the strategy. Sensitivity analysis
may help the decision maker gain insight into which factors of a
decision problem are critical.
Probability
------------------------------------------------------------------
The decision maker in the DriveTek problem may not be confident
about the probability that the electronic approach will be
satisfactory. We refer to the initial probability assignment,
0.5, as the base case. TreePlan can be used to see how the
optimal strategy depends on this factor. The following table was
prepared using TreePlan, printed to a file, and inserted into this
manual with a word processor.
Branch name: Electronic success R = 0
Base probability: 0.50000 Number of event sets: 1
-------------------------------------------------------
Temporary Certainty equivalent Same strategy
probability of optimal strategy as base case?
----------- -------------------- -------------
0.00000 17,000.00 No
0.10000 17,000.00 No
0.20000 17,000.00 No
0.30000 17,000.00 No
0.40000 17,000.00 No
0.50000 20,000.00 Yes
0.60000 26,000.00 Yes
0.70000 32,000.00 Yes
0.80000 38,000.00 Yes
0.90000 44,000.00 Yes
1.00000 50,000.00 Yes
The first line of the heading shows the branch name (which we have
called "Elec OK" on the condensed tree diagrams); "R = 0" means
that certainty equivalents are determined using expected value,
TreePlan User's Manual Page 18
i.e., the decision maker is risk neutral. The second line shows
the base-case probability, 0.5, and notes that there is only one
set of events with this branch name in the decision tree.
Each row in the body of the table shows the results of the
rollback procedure using a different value for the probability of
electronic success. For example, the sixth row shows the results
for the base case when the probability is 0.5.
The fifth row shows the results when the probability of electronic
success is temporarily set equal to 0.4; in this case the
expected value of the optimal strategy is +17K and the optimal
strategy is not the same as the base-case strategy.
To more precisely determine the probability where the strategy
changes, you can use TreePlan to investigate probabilities from
0.4 to 0.5 in steps of 0.01, as shown below.
Branch name: Electronic success R = 0
Base probability: 0.50000 Number of event sets: 1
-------------------------------------------------------
Temporary Certainty equivalent Same strategy
probability of optimal strategy as base case?
----------- -------------------- -------------
0.40000 17,000.00 No
0.41000 17,000.00 No
0.42000 17,000.00 No
0.43000 17,000.00 No
0.44000 17,000.00 No
0.45000 17,000.00 Yes
0.46000 17,600.00 Yes
0.47000 18,200.00 Yes
0.48000 18,800.00 Yes
0.49000 19,400.00 Yes
0.50000 20,000.00 Yes
TreePlan does not indicate ties for the optimal strategy, but if
you view the solved tree when the probability of electronic
success is 0.45, you will see that the rollback certainty
equivalents for "Try elec" and "Try mag" are both equal to +84K.
This sensitivity analysis indicates that if the probability is
below 0.45, the optimal strategy will change. Since 0.45 is very
close to the base-case probability 0.5, the decision maker should
consider the probability of electronic success as a critical
factor in this decision problem.
Chapter 2: Basic Decision Tree Concepts Page 19
Value
------------------------------------------------------------------
The decision maker in the DriveTek problem may want to investigate
the effect of changes in the cost of the mechanical approach. A
sensitivity analysis table using TreePlan is shown below.
Branch name: Use mechanical method R = 0
Base value: -120,000.00 Number of branches: 3
-------------------------------------------------------
Certainty equivalent Same strategy
Temporary value of optimal strategy as base case?
------------------ -------------------- -------------
-120,000.00 20,000.00 Yes
-115,000.00 21,250.00 Yes
-110,000.00 22,500.00 Yes
-105,000.00 23,750.00 Yes
-100,000.00 25,000.00 No
-95,000.00 27,500.00 No
-90,000.00 30,000.00 No
The branch name was called "Use mech" on the condensed tree
diagrams; this branch with partial-cash-flow -120K appears at
three places in the decision tree.
The fifth row in the body of the table shows the results of the
rollback method when the cost of the mechanical method is 100K.
If you use TreePlan to view the solved tree for this case, you
will see that the rollback certainty equivalents for "Use mech"
and "Try elec" are equal. Thus, if the cost of the mechanical
approach is less than 100K (instead of the base-case 120K), the
optimal strategy changes.
TreePlan User's Manual Page 20
Chapter 3: Advanced Decision Tree Concepts
******************************************************************
This chapter discusses some advanced concepts concerning decision
tree models, including risk attitude, utility functions, Bayesian
revision of probabilities, and value of information.
Risk Attitude
==================================================================
In Chapter 2 we reviewed some of the basic concepts concerning
decision tree models, including strategy, payoff distribution, and
certainty equivalent. Recall that a certainty equivalent is a
certain payoff value which is equivalent, for the decision maker,
to a particular payoff distribution. If the decision maker can
determine his or her certainty equivalent for the payoff
distribution of each strategy in a decision tree model, then the
optimal strategy is the one with the highest certainty equivalent.
Unfortunately, it can be difficult to determine one's certainty
equivalent for a complex payoff distribution. We can aid the
decision maker by first determining his or her certainty
equivalent for a simple payoff distribution and then using that
information to infer the certainty equivalent for more complex
payoff distributions.
In Chapter 2 we discussed the circumstances when it is appropriate
for a decision maker to use expected values as certainty
equivalents. If the terminal values in a decision situation are
extreme or if the situation is "one-of-a-kind" so that the outcome
has major implications for the decision maker, an expected value
analysis may not be appropriate. Such situations may require
explicit consideration of risk.
A utility function, U(X), can be used to represent a decision
maker's attitude toward risk. The values or certainty
equivalents, X, are plotted on the horizontal axis; utilities or
expected utilities, U or U(X), are on the vertical axis. You can
use the plot of the function by finding a value on the horizontal
axis, scanning up to the plotted curve, and looking left to the
vertical axis to determine the utility.
A typical utility function might have the general shape shown
below if you draw a smooth curve approximately through the points.
Chapter 3: Advanced Decision Tree Concepts Page 21
U
| *****
| ****
Utility | ***
| ***
or | **
| **
Expected | *
Utility | **
| *
|*
+------------------------- X
Value or
Certainty Equivalent
Since more value means more utility, the inverse, X = X(U), of the
utility function is well-defined, where X is the value or
certainty equivalent corresponding to a utility or expected
utility, U. On the plot of the utility function, you locate a
utility on the vertical axis, scan right to the plotted curve, and
look down to read the corresponding value.
The concept of a payoff distribution or lottery is important for
discussing utility functions. Recall that a payoff distribution
or lottery is a set of payoffs, e.g., X1, X2, and X3, with
corresponding probabilities, P1, P2, and P3.
A fundamental property of a utility function is that the utility
of the certainty equivalent (CE) of a lottery is equal to the
expected utility of the lottery's payoffs, i.e,
U(CE)= P1*U(X1) + P2*U(X2) + P3*U(X3).
It follows that if you compute the expected utility (EU) of a
lottery,
EU = P1*U(X1) + P2*U(X2) + P3*U(X3),
the certainty equivalent of the lottery can be determined using
the inverse of the utility function,
CE = X(EU).
If a utility function has been determined, you can use this
fundamental property to determine the certainty equivalent of any
lottery. First, using a plot of the utility function, locate each
payoff on the horizontal axis and determine the corresponding
utility on the vertical axis. Second, compute the expected
utility of the lottery by multiplying each utility by its
TreePlan User's Manual Page 22
probability and summing the products. Third, locate the expected
utility on the vertical axis and determine the corresponding
certainty equivalent on the horizontal axis.
Instead of using a plot of a utility function, TreePlan uses an
exponential function to represent risk attitude. The general form
of the exponential utility function is
U(X)= A - B*Exp(-R*X).
The parameters A and B determine vertical and horizontal scaling;
R, the risk coefficient, determines the curvature and depends on
the person's risk attitude. Exp is the standard exponential
function, i.e., Exp(Z) represents the value e raised to the power
of Z, where e is the base of the natural logarithms.
After the parameters A, B, and R have been determined, the
exponential utility function and its inverse can be used to
determine the certainty equivalent for any lottery.
TreePlan uses a simple lottery, called a risk attitude assessment
lottery, to determine the decision maker's attitude toward risk.
This lottery has equal probability of obtaining each of the two
payoffs. It is good practice to use a better payoff at least as
large as the highest payoff in the decision problem and a worse
payoff as small or smaller than the lowest payoff; the payoffs
should be far enough apart that the decision maker perceives a
definite difference in the two outcomes. You specify three values
for the fifty-fifty lottery: the Better payoff, the Worse payoff,
and the Certainty Equivalent, as shown below.
+---------------|| Better
Certainty | 0.5 payoff
Equivalent = ()
|
+---------------|| Worse
0.5 payoff
According to the fundamental property of utility functions, the
three values are related as follows.
U(CE)= 0.5*U(Better) + 0.5*U(Worse)
If you use the general form for an exponential utility function
with parameters A, B, and R, and if you simplify terms, it follows
that R must satisfy the following equation.
Exp(-R*CE) = 0.5*Exp(-R*Better) + 0.5*Exp(-R*Worse)
Chapter 3: Advanced Decision Tree Concepts Page 23
Given the values for CE, Better, and Worse, you could use trial-
and-error to find the value of R that exactly satisfies the
equation. TreePlan uses an efficient search procedure (Newton-
Raphson) to find R.
After R is determined, if you want to plot a utility function so
that U(High) = 1.0 and U(Low) = 0.0, you can use the following
formulas to determine the scaling parameters A and B.
A = Exp(-R*Low) / [Exp(-R*Low) - Exp(-R*High)]
B = 1 / [Exp(-R*Low) - Exp(-R*High)]
For the general form of an exponential utility function, the
inverse function X(U) for finding the certainty equivalent CE
corresponding to an expected utility EU is
CE = (-1/R)*Log[(-1/B)*(EU-A)],
where Log(X) represents the natural logarithm of X.
For example, in the DriveTek problem, the maximum and minimum
terminal values are $150,000 and $-50,000, respectively. After
careful consideration of a fifty-fifty lottery with payoffs of
$150,000 and $-50,000, you might decide that you are indifferent
between the lottery and $30,000 for certain, as shown below.
Certainty Better payoff
Equivalent +---------------|| 150,000
| 0.5
30,000 = ()
| Worse payoff
+---------------|| -50,000
0.5
For an exponential utility function to be consistent with this
assessment lottery, R must satisfy
Exp(-30000*R) = 0.5*Exp(-150000*R) + 0.5*Exp(+50000*R).
In this example, TreePlan determines that the equation is
satisfied if R is 0.0000041108.
If you want to plot a utility function with U(-50000) = 0.0 and
U(150000) = 1.0, you can determine the scaling parameters A and B
by substituting the values of R = 0.0000041108, Low = -50000, and
High = 150000 into the formulas. The resulting values are A =
TreePlan User's Manual Page 24
1.784062 and B = 1.4525967, so the appropriate utility function is
U(X) = 1.784062 - 1.4525967*Exp(-0.0000041108*X),
and the inverse, after some simplification, is
CE = -243261.65*Log(1.2281881 - 0.6884223*EU).
This utility function and its inverse can be used to determine
certainty equivalents in the rollback method. For example, when
the DriveTek tree is solved, the event node after the decision
branch "Try magnetic method" corresponds to the following lottery.
Magnetic success
+------------------|| 120,000
| 0.7
()
| Magnetic failure
+------------------|| 0
0.3
Using the general form of the utility function, the utilities of
the payoffs are
U(120000)= 1.784062 - 1.4525967*Exp(-0.0000041108*120000)
= 0.8970912
and
U(0)= 1.784062 - 1.4525967*Exp(-0.0000041108*0)
= 0.3314653,
and the expected utility of the lottery is
EU = 0.7*U(120000) + 0.3*U(0)
= 0.7*0.8970912 + 0.3*0.3314653
= 0.6279638 + 0.0994396
= 0.7274034.
Using the inverse of the general form of the utility function, we
obtain the certainty equivalent of the lottery as follows.
CE = -243261.65*Log(1.2281881 - 0.6884223*0.7274034)
= -243261.65*Log(0.7274274)
= (-243261.65)*(-0.3182411)
= 77416
When the DriveTek tree is solved, the rollback method assigns the
value $77,416 as the certainty equivalent for the event node after
the decision branch "Try magnetic method". TreePlan prints the
Chapter 3: Advanced Decision Tree Concepts Page 25
relevant portion of the solved tree as shown below.
[] 0.700 +120,000
| +------------------------||
| +77,416 | Magnetic success
+------------------------()
Try magnetic method | 0.300 0
+------------------------[]
Magnetic failure
The $77,416 certainty equivalent in this example is consistent
with the risk attitude expressed in the assessment lottery, a
$30,000 certainty equivalent for a fifty-fifty lottery with
payoffs of $150,000 and $-50,000. In both the assessment lottery
and the lottery in this example, the certainty equivalent is less
than the expected value; this risk attitude is called risk
aversion. The table below shows the three categories for risk
attitude, the relationship between the certainty equivalent (CE)
and expected value (ExpVal) of lotteries, and the sign of the risk
coefficient in an exponential utility function.
Risk attitude Lottery Risk coefficient, R
--------------- ----------- -------------------
risk averse CE < ExpVal positive (R > 0)
risk neutral CE = ExpVal zero (R = 0)
risk preferring CE > ExpVal negative (R < 0)
When TreePlan evaluate certainty equivalents in the rollback
method, it ignores the scaling parameters and uses a simplified
form of the exponential utility function and its inverse. The
built-in functions are U(X) = Exp(-R*X) and X(U) = -Log(U)/R,
which yield the same results as the general form. In the risk
neutral situation (labeled R = 0), expected values are used
instead of utilities for computations.
An exponential utility function has a property called "constant
risk aversion." If a fixed amount is added to each payoff of a
lottery, the certainty equivalent increases by the same amount.
(A linear utility function, corresponding to risk neutral attitude
and equivalent to using expected values, also has this property.)
In the assessment lottery of the example, the decision maker has a
$30,000 certainty equivalent for a fifty-fifty lottery with
payoffs of $150,000 and $-50,000. If the decision maker's risk
attitude over a wide range of payoffs can be described by an
exponential utility function, i.e., if the decision maker exhibits
constant risk aversion, the decision maker necessarily has a
TreePlan User's Manual Page 26
$25,000 certainty equivalent for a fifty-fifty lottery with
payoffs of $145,000 and $-55,000 (where $-5,000 has been added to
the payoffs of the assessment lottery). Similarly, he or she has
a $87,416 certainty equivalent for a lottery with a 0.7 chance of
$130,000 and a 0.3 chance of $10,000 (where $10,000 has been added
to the payoffs associated with "Try magnetic method"). For
additional information about constant risk aversion and techniques
for assessing a utility function, please consult the Holloway text
(1979).
An alternative way to specify the main parameter of an exponential
utility function is to use the "risk tolerance," which is the
reciprocal of TreePlan's risk coefficient. For additional
information concerning the use of risk tolerance to characterize
attitude toward risk, please consult the McNamee text (1987).
Sensitivity Analysis
==================================================================
Just as a decision maker may not be completely confident about
preliminary probability assignments and partial-cash-flow
estimates, he or she may not be sure about attitude toward risk.
You can use TreePlan to perform sensitivity analysis to determine
whether or not the optimal strategy is sensitive to changes in
risk attitude. You can express the changes by specifying various
certainty equivalents for the assessment lottery (keeping the
lottery payoffs constant) or by specifying various values for the
risk coefficient directly. If a small change in risk attitude
indicates that a different strategy is optimal, then the decision
maker should think very carefully about risk attitude before
implementing the strategy.
Lottery Certainty Equivalent
------------------------------------------------------------------
The decision maker in the DriveTek problem may not be confident
that expected values should be used for certainty equivalents. We
could refer to the risk neutral situation as the base case, using
a $50,000 certainty equivalent for a fifty-fifty assessment
lottery with payoffs of $150,000 and $-50,000. You can use
TreePlan to see how the optimal strategy depends on the certainty
equivalent of the assessment lottery. The following table was
prepared using TreePlan, printed to a file, condensed with a word
processor, and inserted into this manual.
Chapter 3: Advanced Decision Tree Concepts Page 27
Base lottery CE: 50,000.00 Better payoff: 150,000.00
Base risk coefficient: 0 Worse payoff: -50,000.00
----------------------------------------------------------------
Temporary lottery Temporary Cert. equiv. Same strategy
cert. equiv. risk coeff. of opt. strat. as base case?
----------------- -------------- -------------- -------------
50,000.00 + 0.0000000000 20,000.00 Yes
45,000.00 + 0.0000010017 16,709.62 Yes
40,000.00 + 0.0000020135 13,525.43 Yes
35,000.00 + 0.0000030460 10,428.80 Yes
30,000.00 + 0.0000041108 7,402.04 Yes
25,000.00 + 0.0000052213 4,428.02 Yes
20,000.00 + 0.0000063933 1,865.95 No
15,000.00 + 0.0000076463 0.00 No
10,000.00 + 0.0000090054 0.00 No
5,000.00 + 0.0000105038 0.00 No
0.00 + 0.0000121876 0.00 No
On the upper-right side of the heading, the first and second lines
show the payoffs of the risk attitude assessment lottery, which
applies to all cases shown in the table. The upper-left side of
the heading shows the certainty equivalent of the assessment
lottery that specifies the base case for the table; the heading
also shows the associated risk coefficient for the base case.
Each row in the body of the table shows the results of the
rollback procedure using a different value for the certainty
equivalent of the assessment lottery. For example, the first row
shows the results for the base case when the certainty equivalent
of the assessment lottery is $50,000. The fifth row shows the
results when the lottery's certainty equivalent is $30,000, which
is the situation described in the Risk Attitude section of this
chapter. For both cases, the strategy "Prepare; Try elec" is
optimal.
The seventh row shows the results when the certainty equivalent is
$20,000; in this case the certainty equivalent of the optimal
strategy is $1,865.95, and the optimal strategy is not the same as
the base-case strategy.
Additional sensitivity analyses (not shown) reveal that the
strategy "Prepare; Use mech" is optimal if the decision maker's
certainty equivalent of the assessment lottery is less than
$23,089. Further sensitivity analyses (not shown) indicate that
if the decision maker's certainty equivalent of the assessment
lottery is less than $16,087, the strategy "Don't prepare
proposal" is optimal.
To summarize, the strategy "Prepare; Try electronic method" is
TreePlan User's Manual Page 28
optimal for a risk neutral decision maker, "Prepare; Use
mechanical method" is optimal for a decision maker who is somewhat
risk averse, and "Don't prepare proposal" is optimal for a very
risk averse decision maker.
Risk Coefficient
------------------------------------------------------------------
You can also use TreePlan to perform sensitivity analysis to
determine whether or not the optimal strategy is sensitive to
changes in risk attitude by specifying various values for the risk
coefficient directly. A condensed sensitivity analysis table
using TreePlan is shown below.
Base lottery CE: 50,000.00 Better payoff: 150,000.00
Base risk coefficient: 0 Worse payoff: -50,000.00
----------------------------------------------------------------
Temporary lottery Temporary Cert. equiv. Same strategy
cert. equiv. risk coeff. of opt. strat. as base case?
----------------- -------------- -------------- -------------
50,000.00 + 0.0000000000 20,000.00 Yes
45,008.31 + 0.0000010000 16,714.99 Yes
40,065.96 + 0.0000020000 13,566.83 Yes
35,219.74 + 0.0000030000 10,563.30 Yes
30,511.63 + 0.0000040000 7,709.05 Yes
25,977.10 + 0.0000050000 5,005.86 Yes
21,644.12 + 0.0000060000 2,633.85 No
17,532.82 + 0.0000070000 696.22 No
13,655.80 + 0.0000080000 0.00 No
10,018.84 + 0.0000090000 0.00 No
6,621.92 + 0.0000100000 0.00 No
The interpretation of the heading and cases in this table is the
same as that in the previous table.
The base strategy is "Prepare proposal; Try electronic method,"
corresponding to a zero risk coefficient. Additional sensitivity
analyses (not shown) reveal that the strategy "Prepare proposal;
Use mechanical method" is optimal if the decision maker's risk
coefficient is less than 0.0000056610, and the strategy "Don't
prepare proposal" is optimal if the risk coefficient is less than
0.0000073658.
Chapter 3: Advanced Decision Tree Concepts Page 29
Expected Value of Perfect Information
==================================================================
Although we seldom have the opportunity to obtain perfect
information, the expected value of perfect information is a useful
measure because it is the upper limit on the value of any
additional information in a decision problem. We can determine
this measure by comparing the expected value of the optimal
strategy when a perfect prediction is available with the expected
value without the perfect information; the difference is the
value of the information itself.
The following definitions and abbreviations are useful for
discussing this topic.
EVUU = Expected Value Under Uncertainty, the expected value
of the optimal strategy without perfect information
EVPP = Expected Value with Perfect Prediction, the expected
value of the optimal strategy when perfect information is
available
EVPI = Expected Value of Perfect Information, the difference
between EVPP and EVUU
EVPI = EVPP - EVUU
The following problem, adapted from an example in the Bierman text
(1991), will be used to illustrate the basic concepts of value of
information and Bayesian revision of probabilities.
Valley Problem (A)
==================================================================
Valley Products, Inc., has developed a new product and must decide
whether to spend $3 million to introduce it. The market potential
is uncertain, and Valley has characterized the possible sales as
either high or low. If the product is a success, sales will be
high, with net $7 million (sales revenues minus all costs except
initial introduction); if the product is a flop, sales will be
low, with net $1 million. Valley thinks there is a 30% chance of
high sales and a 70% chance of low sales.
A condensed version of the unsolved decision tree model for the
Valley problem (sample tree data file VALLEY_A.TRE), is shown
below. Partial-cash-flows and terminal values are in millions of
dollars. (The diagram was prepared using TreePlan, printed to a
file, and condensed with a word processor.)
TreePlan User's Manual Page 30
High sales
+------------|| +4.00
Introduce | +7.00 0.30
+------------()
| -3.00 | Low sales
| +------------|| -2.00
[] +1.00 0.70
|
| Don't
+------------||.............. 0
0.00
A condensed version of the solved decision tree (rollback
certainty equivalents at the left of each node) for the Valley
problem is shown below.
0.30 +4.00
+------------|| +4.00
-0.20 | High sales
+------------()
| Introduce | 0.70 -2.00
| +------------|| -2.00
[] Low sales
|
| 0.00
+============||.............. 0
Don't
The expected value of the strategy "Introduce" is $-0.2 million,
and the optimal strategy is "Don't introduce" with zero expected
value.
In the Valley problem, the expected value under uncertainty (EVUU)
is zero. We will compare this expected value (obtained with no
additional information) with expected values obtained with perfect
and imperfect predictions.
Valley EVPI Tree
==================================================================
To determine the value of information, TreePlan constructs an
expanded EVPI tree. A condensed version of the unsolved EVPI
tree, showing partial-cash-flow values below each branch, is shown
below.
Chapter 3: Advanced Decision Tree Concepts Page 31
High sales
+------------||.............. +4.00
Introduce | +7.00 0.30
+------------()
| -3.00 | Low sales
No info | +------------||.............. -2.00
+------------[] +1.00 0.70
| 0.00 |
| | Don't
| +------------||............................ 0
| 0.00
|
| High sales
| +------------|| +4.00
| Introduce | +7.00 1.00
[] +------------()
| | -3.00 | Low sales
| "High" | +------------|| -2.00
| +------------[] +1.00 0.00
| | 0.00 0.30 |
| | | Don't
| | +------------||.............. 0
| | 0.00
| Perf. info |
+------------() High sales
0.00 | +------------|| +4.00
| Introduce | +7.00 0.00
| +------------()
| | -3.00 | Low sales
| "Low" | +------------|| -2.00
+------------[] +1.00 1.00
0.00 0.70 |
| Don't
+------------||.............. 0
0.00
The top section of the tree following the decision branch "No
info" shows the original Valley problem when no additional
information is available.
The major portion of the tree following the decision branch "Perf.
info" shows the decision and event branches associated with using
a perfect prediction. Since Valley thinks there is a 30% chance
of high sales, the probability that the perfect predictor will say
"High sales" is 0.3. After a prediction of "High" or "Low" is
received, Valley must decide whether to introduce the product. If
the perfect prediction was "High," the probability of high sales
TreePlan User's Manual Page 32
is 1.0; if the prediction was "Low," the chance of high sales is
zero.
A condensed version of the solved EVPI tree for the Valley problem
is shown below. Rollback certainty equivalents (expected values)
are shown on the left side of each node.
0.30 +4.00
+------------||.............. +4.00
-0.20 | High sales
+------------()
| Introduce | 0.70 -2.00
0.00 | +------------||.............. -2.00
+------------[] Low sales
| No info |
| | 0.00
| +------------||............................ 0
| Don't
|
| 1.00 +4.00
| +============|| +4.00
| +4.00 | High sales
[] +============()
| | Introduce | 0.00 -2.00
| 0.30 +4.00 | +------------|| -2.00
| +============[] Low sales
| | "High" |
| | | 0.00
| | +------------||.............. 0
| | Don't
| +1.20 |
+============() 0.00 +4.00
Perf. info | +------------|| +4.00
| -2.00 | High sales
| +------------()
| | Introduce | 1.00 -2.00
| 0.70 0.00 | +------------|| -2.00
+============[] Low sales
"Low" |
| 0.00
+============||.............. 0
Don't
In the Valley EVPI trees, we have assumed that the perfect
prediction is free. The optimal strategy is to obtain the perfect
information; if the prediction is "High," introduce the product;
if the prediction is "Low," don't introduce. The expected value
of the optimal strategy using the perfect prediction is $1.2
Chapter 3: Advanced Decision Tree Concepts Page 33
million.
The expected value of perfect information is determined as
follows.
EVPI = EVPP - EVUU
= $1.2 million - $0
= $1.2 million
If the cost of the perfect prediction is $1.2 million (partial-
cash-flow -1.20 on the branch "Perf. info"), all terminal values
in that portion of the tree will be decreased by 1.20. When the
tree if solved, all rollback certainty equivalents will also be
decreased by 1.20, and the expected value associated with using
the perfect prediction will be 0. Therefore, if the cost is $1.2
million, Valley will be indifferent between using the perfect
prediction and acting without any additional information. Thus,
the maximum that Valley should be willing to pay for information
in this problem is $1.2 million.
When you use TreePlan to determine EVPI, TreePlan automatically
constructs an expanded tree, solves it using the rollback method
with expected values, computes EVPI as the difference between the
expected value of the best strategy with no additional information
(your original problem) and the expected value of the best
strategy using a perfect prediction, and displays EVPI in the
lower left corner of the screen.
Bayesian Revision of Probabilities
==================================================================
Decision problems involving the option to gather information
usually have the following general structure.
+-------- +-------- +-------- +--------
[]-------- ()-------- []-------- ()--------
+-------- +-------- +-------- +--------
Info Info Main Main
Decision Event Decision Event
For example, in the Valley EVPI tree, the info decision is whether
to act without additional information or use the perfect
prediction; the info event is a prediction of "High" or "Low;"
the main decision is whether to introduce the product or not; the
main event is actual high sales or low sales. The EVPI tree
TreePlan User's Manual Page 34
describes a hypothetical situation; realistic decision problems
involve imperfect predictions where the information-gathering
options have a similar structure.
To analyze a decision problem of this kind, the probabilities
required for the decision tree may not be available directly. We
may have to perform Bayesian revision of probabilities before
using the rollback method to solve the tree. For Bayesian
analysis, TreePlan uses the terms shown in the following table.
Probability Bayesian Name General Type
-------------- ------------- ----------------
P(Main) Prior Simple, Marginal
P(Info | Main) Likelihood Conditional
P(Main & Info) Joint
P(Info) Preposterior Simple, Marginal
P(Main | Info) Posterior Conditional
"Main" refers to the set of events that directly affect the
payoffs, i.e., the major uncertainties that we would like to
predict. In Bayesian terms, P(Main) is a "Prior" probability,
i.e., the probability of a main event prior to obtaining any
additional information. In general terms, P(Main) may be called a
simple, marginal, or unconditional probability. In Valley's
original problem, P(High) = 0.3 and P(Low) = 0.7 are examples of
P(Main). The original problem, before considering any
information-gathering options, is sometimes referred to as the
"prior problem."
"Info" refers to the set of events that are the results of the
information-gathering effort. In Bayesian terms, P(Main | Info)
is a "Posterior" probability, i.e., the probability of a main
event conditional on a result of the information-gathering
activity. In general terms, P(Main | Info) is a conditional
probability. In Valley's EVPI problem, P(High | "High") = 1.0 is
an example of a posterior probability.
Bayesian revision involves using the prior probabilities and other
probabilities expressing the reliability of the information-
gathering activity to obtain the posterior probabilities that are
needed for the decision tree. In a sense, the prior probabilities
are "revised," after receiving information, to become posterior
probabilities.
In Bayesian terms, P(Info | Main) is a "Likelihood" probability,
i.e., the probability of a info event conditional on a main event.
In general terms, P(Info | Main) is a conditional probability.
The likelihoods are a way of showing the relationship between the
Chapter 3: Advanced Decision Tree Concepts Page 35
info events and the main events, thereby measuring the reliability
or accuracy of the information. In other words, likelihoods are a
way of expressing how well the info events predict the main
events.
Bayesian revision uses priors and likelihoods as inputs and
produces posteriors as one of the outputs. Priors measure our
original state of information; likelihoods measure the accuracy
of the information; posteriors measure our state of information
after receiving the information.
In Bayesian terms, P(Info) is a "Preposterior" probability, i.e.,
the probability of an information-gathering result. In general
terms, P(Info) may be called a simple, marginal, or unconditional
probability. Preposteriors are another output of Bayesian
revision. Preposteriors appear on the decision tree and precede
the posterior probabilities, thus the name.
A fifth kind of probability involved in Bayesian revision is
"Joint" probability, P(Main & Info). Joints are an intermediate
step in the revision process; they do not appear on the decision
tree.
Using Bayesian terms, the following diagram shows how the
probabilities are related.
Priors --------> +--------+ ---> Preposteriors ---> +------------+
| Joints | | Posteriors |
Likelihoods ---> +--------+ ----------------------> +------------+
Joints are calculated from Likelihoods and Priors.
Preposteriors are calculated from Joints.
Posteriors are calculated from Joints and Preposteriors.
Using probability notation, the relationships and formulas are
shown below.
TreePlan User's Manual Page 36
P(Main) -------> +--------------+ --> P(Info) --> +--------------+
| P(Info&Main) | | P(Main|Info) |
P(Info|Main) --> +--------------+ --------------> +--------------+
P(Info & Main) = P(Info | Main) * P(Main)
P(Info) = Sum of P(Info & Main)
P(Main | Info) = P(Info & Main) / P(Info)
The calculations can be organized by substituting into the
formulas, setting up a table, or drawing probability trees. Also,
you could combine the three formulas into a single formula (not
shown here), called "Bayes' rule," where the posteriors
P(Main|Info) are expressed as a function of the priors P(Main)
and likelihoods P(Info|Main).
TreePlan uses probability trees for displaying the inputs,
intermediate results, and outputs of Bayesian revision. If you do
the computations using probability trees, you can divide the work
into eight steps.
(1) Construct a probability tree for the inputs. First draw
branches for the set of Main events. After each Main event
branch, draw a set of branches for the Info events. Label
each branch.
(2) Write the prior probabilities on the input tree (on the set
of branches on the left).
(3) Write the likelihoods on the input tree (on each set of
branches on the right).
(4) Multiply each prior times the following likelihood, and write
the resulting joint probability near the far right endpoints
of the probability tree.
The "Inputs and Joints" probability tree, sometimes called
"Nature's tree," resembles the following diagram.
+--- P(Info | Main) --- P(Info & Main)
+---- P(Main) -----()
| +----------------------
()
| Priors +----------------------
+------------------() Likelihoods
+---------------------- Joints
Chapter 3: Advanced Decision Tree Concepts Page 37
(5) Construct a probability tree for the outputs. First draw
branches for the set of Info events. After each Info event
branch, draw a set of branches for the Main events. Label
each branch.
(6) Copy each joint probability from the input tree to the
appropriate endpoint of the output tree; the order will be
different.
(7) Compute preposteriors by summing the joint probabilities
following each Info event branch. Write a preposterior on
each Info event branch.
(8) Compute each posterior by dividing a joint probability by the
preposterior that precedes it on the tree. Write a posterior
on each Main event branch.
The "Outputs and Joints" probability tree resembles the following
diagram.
+--- P(Main | Info) --- P(Info & Main)
+---- P(Info) -----()
| +----------------------
()
| Preposteriors +----------------------
+------------------() Posteriors
+--------------------- Joints
(In some decision problems, joint probabilities may be used
instead of likelihoods to express the accuracy of the information.
If the joints and priors are consistent, only steps 5 through 8 of
the Bayesian revision process are required. If not, the joints
can be used to determine likelihoods, which are combined with
priors using Bayesian revision using all eight steps.)
Valley Problem (B)
==================================================================
Valley has the opportunity to conduct a market survey before
deciding whether to introduce the product. The survey will cost
$0.2 million, and there are three possible results: a "Success"
prediction for the new product, indicating high sales; a
"Failure" prediction, indicating low sales; or an "Uncertain"
prediction (an inconclusive survey result). However, the survey
TreePlan User's Manual Page 38
is imperfect. Even if the survey predicts success, there is a
chance that sales will actually be low; if it predicts failure,
sales may be high. Based on past experience and modified by
personal judgment, Valley has quantified the survey's reliability
by assigning the following likelihoods.
Likelihoods, P(Info | Main)
(Main event)
Actual sales
(Info event) ------------
Survey prediction High Low
----------------------- ---- ---
Survey predicts Success 0.4 0.1
Survey is Uncertain 0.4 0.5
Survey predicts Failure 0.2 0.4
--- ---
1.0 1.0
The table of likelihoods shows two probability distributions, one
conditional on High sales and one conditional on Low sales. For
example, the 0.2 in the lower left corner of the table is the
probability that the survey predicts Failure, conditional on
actual sales being High; the 0.1 in the upper right corner is the
probability that the survey predicts Success, conditional on
actual sales being Low. In an accurate survey, each of these
likelihoods is close to zero.
Although the survey is imperfect, its cost is less than $1.2
million (EVPI), so further analysis is justified.
The following tree diagram, obtained using TreePlan's Zoom File
option, shows the structure of the decision problem.
Chapter 3: Advanced Decision Tree Concepts Page 39
+-HighSales-||
+-Introduce-()
+-No info---[] +-Low sales-||
| |
| +-Don't-----||
|
| +-HighSales-||
| +-Introduce-()
[] +-Success---[] +-Low sales-||
| | |
| | +-Don't-----||
| |
| | +-HighSales-||
| | +-Introduce-()
+-Survey----()-Uncertain-[] +-Low sales-||
| |
| +-Don't-----||
|
| +-HighSales-||
| +-Introduce-()
+-Failure---[] +-Low sales-||
|
+-Don't-----||
The tree has the general structure of an information-gathering
decision problem.
Info Decision No info or Survey
Info Event Success, Uncertain, or Failure
Main Decision Introduce or Don't
Main Event High sales or Low sales
Starting with the sample tree data file VALLEY_A.TRE, you can
develop the decision tree shown above by using TreePlan's EVPI
Retain option and renaming "High sales" to "Success" and "Low
sales" to "Uncertain." Then use the Node Add option to obtain the
"Failure" branch and the Node Copy option to finish the tree. The
result is sample tree data file VALLEY_B.TRE.
Using TreePlan, you use the Bayes Link Main-event option to select
the Main event node (preceding High sales and Low sales), and you
use the Bayes Link Info-event option to select the Info event node
(preceding Success, Uncertain, and Failure). Then you use the
Bayes Input option to enter the priors (0.3 and 0.7) and
likelihoods (from the table above) on a probability tree diagram.
The following diagram shows the inputs and the joint probabilities
computed by TreePlan.
TreePlan User's Manual Page 40
Prior Likelihood Joint
==================================================================
Success 0.40000
+-------------------------- 0.12000
|
High sales 0.30000 | Uncertain 0.40000
+--------------------------()-------------------------- 0.12000
| |
| | Failure 0.20000
| +-------------------------- 0.06000
()
| Success 0.10000
| +-------------------------- 0.07000
| |
| Low sales 0.70000 | Uncertain 0.50000
+--------------------------()-------------------------- 0.35000
|
| Failure 0.40000
+-------------------------- 0.28000
TreePlan also computes the preposteriors and posteriors. You use
the Bayes Screen option to view the inputs and outputs of Bayesian
revision, shown above and below. These diagrams were obtained
using the Bayes File option.
Preposterior Posterior Joint
==================================================================
High sales 0.63158
Success 0.19000 +-------------------------- 0.12000
+--------------------------()
| | Low sales 0.36842
| +-------------------------- 0.07000
|
| High sales 0.25532
| Uncertain 0.47000 +-------------------------- 0.12000
()--------------------------()
| | Low sales 0.74468
| +-------------------------- 0.35000
|
| High sales 0.17647
| Failure 0.34000 +-------------------------- 0.06000
+--------------------------()
| Low sales 0.82353
+-------------------------- 0.28000
Chapter 3: Advanced Decision Tree Concepts Page 41
After Bayesian revision, you use the Bayes Transfer option to
transfer the probabilities to the decision tree. Then use the
Solve option to determine the optimal strategy.
The Valley Solved Tree diagram, shown below, is a condensed
version of the solved tree, showing rollback certainty equivalents
to the left of each node. In this diagram, the survey partial-
cash-flow (-0.20, in millions of dollars) is included in
appropriate terminal values. The optimal strategy is: Take the
survey; if the survey predicts Success, Introduce the product;
if the survey prediction is Uncertain or Failure, Don't introduce.
The net gain of the Survey strategy over the No info strategy is
0.14 - 0.00 = 0.14, or $140,000.
TreePlan User's Manual Page 42
Valley Solved Tree
==================================================================
0.30 +4.00
+------------||.............. +4.00
-0.20 | High sales
+------------()
| Introduce | 0.70 -2.00
0.00 | +------------||.............. -2.00
+------------[] Low sales
| No info |
| | 0.00
| +------------||............................ 0
| Don't
|
| 0.63 +3.80
| +============|| +3.80
| +1.59 | High sales
| +============()
| | Introduce | 0.37 -2.20
| 0.19 +1.59 | +============|| -2.20
[] +============[] Low sales
| | Success |
| | | -0.20
| | +------------||.............. -0.20
| | Don't
| |
| | 0.26 +3.80
| | +------------|| +3.80
| | -0.67 | High sales
| | +------------()
| | | Introduce | 0.74 -2.20
| +0.14 | 0.47 -0.20 | +------------|| -2.20
+============()============[] Low sales
* Survey | Uncertain |
| | -0.20
| +============||.............. -0.20
| Don't
|
| 0.18 +3.80
| +------------|| +3.80
| -1.14 | High sales
| +------------()
| | Introduce | 0.82 -2.20
| 0.34 -0.20 | +------------|| -2.20
+============[] Low sales
Failure |
| -0.20
+============||.............. -0.20
Don't
Chapter 3: Advanced Decision Tree Concepts Page 43
Expected Value of Sample Information
==================================================================
An alternative approach borrows some terminology from statistical
decision theory, where we loosely interpret "sampling" as any
information-gathering activity that yields an imperfect
prediction. The following definitions and abbreviations are
useful for this discussion.
EVUU = Expected Value Under Uncertainty, the expected value
of the optimal strategy without perfect information
EVSP = Expected Value with Sample Prediction, the expected
value of the optimal strategy when imperfect information is
available, assuming it's free
EVSI = Expected Value of Sample Information, the difference
between EVSP and EVUU
ENGS = Expected Net Gain from Sampling, the difference
between EVSI and the cost of sampling (the cost of the imperfect
information)
EVSI = EVSP - EVUU
ENGS = EVSI - Cost
EVSI may be interpreted as the maximum amount a risk-neutral
decision maker is willing to pay for the imperfect information,
and ENGS is the net gain from using the imperfect information over
acting without additional information. If ENGS is negative, a
risk-neutral decision maker should not use the information-
gathering activity; the cost of the information exceeds its value.
The Valley EVSI Tree diagram below shows the results for this
alternative approach, where the survey is assumed to be free. The
Expected Value with Sample Prediction is the rollback value for
the Survey($0) option; EVSP = 0.34, in millions of dollars. In
this example, we have the following results.
EVSI = 0.34 - 0.00 = 0.34
ENGS = 0.34 - 0.20 = 0.14
A risk-neutral decision maker is willing to pay a maximum of
TreePlan User's Manual Page 44
$340,000 for the survey. The survey cost is $200,000, so the net
gain from using the survey is $140,000.
Chapter 3: Advanced Decision Tree Concepts Page 45
Valley EVSI Tree
==================================================================
0.30 +4.00
+------------||.............. +4.00
-0.20 | High sales
+------------()
| Introduce | 0.70 -2.00
0.00 | +------------||.............. -2.00
+------------[] Low sales
| No info |
| | 0.00
| +------------||............................ 0
| Don't
|
| 0.63 +4.00
| +============|| +4.00
| +1.79 | High sales
| +============()
| | Introduce | 0.37 -2.00
| 0.19 +1.79 | +============|| -2.00
[] +============[] Low sales
| | Success |
| | | 0.00
| | +------------||.............. 0
| | Don't
| |
| | 0.26 +4.00
| | +------------|| +4.00
| | -0.47 | High sales
| | +------------()
| | | Introduce | 0.74 -2.00
| +0.34 | 0.47 0.00 | +------------|| -2.00
+============()============[] Low sales
Survey($0) | Uncertain |
| | 0.00
| +============||.............. 0
| Don't
|
| 0.18 +4.00
| +------------|| +4.00
| -0.94 | High sales
| +------------()
| | Introduce | 0.82 -2.00
| 0.34 0.00 | +------------|| -2.00
+============[] Low sales
Failure |
| 0.00
+============||.............. 0
Don't
TreePlan User's Manual Page 46
Risk Attitude and Value of Information
==================================================================
So far we have discussed the value of perfect and imperfect
information for a risk neutral decision maker. Determining the
value of information for a decision maker who is not risk neutral
can be more difficult.
If a decision maker has an arbitrary utility function (not
exponential) and we want to determine the value of information, we
construct a decision tree showing both the original decision
problem (with no additional information) and the information-
gathering activity. After constructing the tree, complete with
probabilities and partial-cash-flow values, we repeatedly use the
rollback method to solve the tree using different information-
gathering costs. Each time the tree is solved, we compute
terminal values including the information-gathering cost, and we
use the arbitrary utility function to determine certainty
equivalents for the rollback method. We try to find an
information-gathering cost so that the certainty equivalent of the
optimal strategy of the original problem (with no additional
information) equals the certainty equivalent of the optimal
strategy for the information-gathering activity. When our search
finds such a cost, we have determined the value of information,
i.e., the maximum the decision maker should be willing to pay for
the information.
The unsolved Valley EVPI tree is an example of a tree for
determining the value of perfect information, and the unsolved
Valley EVSI tree could be used for determining the value of
imperfect information. To search for the value of information, we
would try various partial-cash-flow values for the "Use perfect
prediction" branch or the "Survey" branch. Since TreePlan's
built-in utility function is exponential, we would have to use
hand calculations for the rollback method with the decision
maker's arbitrary utility function.
However, if the decision maker's utility function is exponential,
TreePlan can be used to determine the value of information using
the same approach we used for a risk neutral decision maker. We
assume the information is free, solve the tree using the
appropriate value for the risk coefficient R, and subtract the
certainty equivalent of the no-information strategy from the
certainty equivalent of the information-gathering strategy; the
difference is the value of information.
Chapter 3: Advanced Decision Tree Concepts Page 47
The simplified approach for this special case is appropriate due
to the "constant risk aversion" property of exponential utility
functions (discussed in the Risk Attitude section of this
chapter): If a fixed amount is added to each payoff of a lottery,
the certainty equivalent increases by the same amount. Likewise,
if the value of information is subtracted from the values of the
payoff distribution of the information-gathering strategy, the
certainty equivalent will be reduced by the same amount, and the
decision maker will be indifferent between the no-information
strategy and the information-gathering strategy.
TreePlan's EVPI option covers only the risk neutral situation. To
determine the value of perfect information using an exponential
utility function, follow these steps.
(1) Use the Node options to construct the original problem (the
prior problem).
(2) Use the EVPI Retain option to construct the expanded tree.
(3) Use the Solve Risk options to express risk attitude.
(4) Use the Solve View option to determine certainty equivalents
for the "No additional info" and "Use perfect prediction"
strategies.
(5) Subtract the certainty equivalents to obtain the value of
perfect information.
You can use a similar approach to determine the value of imperfect
information using an exponential utility function.
TreePlan User's Manual Page 48
Chapter 4: General Treeplan Features
******************************************************************
This chapter discusses some general TreePlan features, including
the screen layout, modes, and tree navigation.
It will be worthwhile to view an existing decision tree on
TreePlan's screens while you read the following sections. Follow
these steps.
(1) Run TreePlan. (If necessary, refer to the section "Starting
and stopping TreePlan" at the end of Chapter 1.)
(2) Wait for the READY mode indicator to appear in the top right
corner of the screen.
(3) Type / F R to display a menu of tree files. (Pressing the
slash key displays the main menu; F selects the File
submenu; and R tells TreePlan you want to Retrieve a file.)
(4) Use the arrow keys to highlight the file named DRIVETEK.TRE,
and press the RETURN key to select it.
If you make a mistake, press the Escape key several times until
the READY mode indicator appears; then start over.
Screen Layout
==================================================================
This section explains TreePlan's screen layout and some of its
associated terminology. In READY mode, the screen is divided into
several sections as shown below.
+------------------------------------------+
| Current field info |Mode|
|------------------------------------------|
| Previous | +------------ |
| branches | | |
| | ---- Tree display ----- |
| | | |
| | +------------ |
|------------------------------------------|
| Messages |TreePlan|
+------------------------------------------+
Chapter 4: General TreePlan Features Page 49
Mode
The mode indicator in the upper right corner shows TreePlan's
current operating condition. For example, in the READY mode, you
can view the entire tree by using the pointer keys; in the MENU
mode, you can select options from the menu. The mode often
changes when you begin an action, such as executing a command or
making an entry.
Tree display
The main portion of the screen is the tree display which shows two
stages of the decision tree in diagram form. Details are shown
for all branches on the right side and for one center branch
leading to that point. Only branch names are shown for the other
center branches. Each stage can have a maximum of five branches.
Field
A field is a part of the tree that can store data. Each branch
has a name field and a partial-cash-flow value field; event
branches also have a probability field. The length of the name
field is 22 characters, and the length of the probability field is
4 to 7 characters, depending on the format you select. The length
of the partial-cash-flow value field, which also depends on the
probability format you select, is 14 to 17 characters. A field is
uniquely identified by its type and the branch names on the path
from the start of the tree to its location.
Field pointer
The field pointer is a rectangular highlight that appears on one
field of the tree display and identifies it as the current field.
You can move the field pointer to any field in the tree; your
next entry or procedure affects this field. For example, typing
an entry or executing certain commands affects the current field.
Current field info
In READY mode, the top three lines show information about the
current field. The first line shows the kind of field, either
name, value, or probability, and its contents.
If you start typing to replace the contents of a field, the
characters you type are shown on the second line, directly below
the current contents of the field. If you press F2 to edit a
TreePlan User's Manual Page 50
field, the second line initially shows the current contents with
the cursor after the last character. The third line uses carets
to show the maximum length of the field.
Previous branches
This section shows a list of names for the branches that precede
those currently shown on the tree display.
Messages
An error message is displayed on the bottom line of the screen
when TreePlan has detected a problem. Press Enter or Escape to
resume.
Menus
In MENU mode, the current field info in the top three lines is
replaced by menu information. The first line shows the menu path,
i.e., the menu and submenu options you have already chosen. The
second line shows the current menu with the commands or options
currently available for selection. The third line shows either a
one-line description of the command currently highlighted on the
menu or a list of options available from a submenu.
TreePlan Modes
==================================================================
The mode indicator in the upper right corner shows TreePlan's
current operating condition. Explanations for TreePlan's eight
modes are shown below.
Mode Explanation
READY TreePlan is ready to do something. Use pointer keys to
move the highlighted field pointer; press F2 to edit a
field, or simply start typing to replace contents of a
field; press / for the main menu. This mode is used
to view an unsolved tree and to change branch names,
values, and probabilities.
MENU Commands or options are displayed on the second line of
the display. Use arrow keys to highlight an option and
press Enter to select, or type the first letter of the
option.
Chapter 4: General TreePlan Features Page 51
INSERT While editing an entry, characters you type are
inserted at the cursor position.
OVERTYPE While editing an entry, characters you type overwrite
the contents at the cursor position. Press the Insert
key to switch between insert and overtype modes.
POINT Use pointer keys to move the highlighted pointer; then
press Enter to select. This mode is often used to
select a field as part of a command.
VIEW Use pointer keys to view; when finished, press Enter
or Escape. This mode is often used to view the results
of a command operation.
WAIT TreePlan is busy performing a task. You may see this
mode when TreePlan is accessing a disk or performing
calculations.
BAYES Use pointer keys to move the highlighted field pointer;
press F2 to edit a field, or simply start typing to
replace contents of a field; press Enter or Escape
when finished. This mode is used only for inputting
Bayes probabilities.
ERROR TreePlan has detected a problem. An error message is
shown on the bottom line of the display. Press Enter
or Escape to resume.
Tree Navigation In READY Mode
==================================================================
This section of the manual explains how to view a tree in READY
mode. The commands for building a tree are discussed in a later
section.
TreePlan uses the following seven special keys as "pointer keys"
in READY, VIEW, and POINT modes: Page-Up, Page-Down, Home, Up-
arrow, Down-arrow, Left-arrow, and Right-arrow. These keys are
usually located on the right side of a computer keyboard
It will be worthwhile to view the DriveTek decision tree on
TreePlan's screens while you read this section. Follow the steps
on the first page of this chapter to run TreePlan and retrieve the
DriveTek file (/FR). If you're already viewing the tree, press
the Home key to move to the initial branches. A condensed version
of the display is shown below.
TreePlan User's Manual Page 52
Awarded
Previous Branches +---------------[D]
----------------- Prepare | +250,000 0.5
(None) [D]---------------(E)
| -50,000 | No award
| +---------------|T|
+-Don't 0 0.5
To move the highlighted field pointer from field to field, use the
four arrow keys: Right-arrow, Left-arrow, Up-arrow, and Down-
arrow.
You can think of the center and right sections of the tree display
as being a window for viewing sections of the complete tree. If
you continue to press the Right-arrow key or the Left-arrow key
when the pointer is at the boundary of the window, the window
shifts to show another section of the tree.
For example, if you press the Home key and then press the Right-
arrow key two or three times, the window moves to show the
branches shown below.
Use mech
+---------------|T|
| -120,000
Previous Branches |
----------------- Awarded | Try elec
Prepare (E)---------------[D]---------------(E)
| +250,000 0.5 | -50,000
| |
+-No award | Try mag
+---------------(E)
-80,000
If you continue to press the Right-arrow key (starting from Home,
press the Right-arrow key four times), you will see the following
tree display.
Chapter 4: General TreePlan Features Page 53
Previous Branches Terminal
----------------- Value
Prepare Use mech
Awarded [D]---------------|T| +80,000
| -120,000
|
+-Try elec
|
+-Try mag
If you press the Right-arrow key more than four times (starting
from Home), you will hear a "bump" sound, indicating that you have
reached an extremity of the tree. You cannot move the field
pointer to the terminal value. The terminal value is the sum of
the partial-cash-flow values on the three branches leading to the
terminal node: Prepare, Awarded, and Use mech, with values
-50,000, +250,000, and -120,000, whose sum is +80,000.
You can use the Page-Up and Page-Down keys to change the branch
shown in detail in the center section of the tree display. For
example, if you start at Home and press the Right-arrow key four
times so that you see the display shown above and then press the
Page-Down key once, the display changes to show the details of the
"Try elec" branch as shown below.
Previous Branches +-Use mech Elec success
----------------- | +---------------|T|
Prepare | Try elec | 0 0.5
Awarded [D]---------------(E)
| -50,000 | Elec failure
| +---------------[D]
+-Try mag 0 0.5
The Page-Up and Page-Down keys affect the branches shown in the
center section, even if the field pointer is in the right section
of the display. If the field pointer is in the center section,
you can also use the Up-arrow and Down-arrow keys to change the
branch shown in detail in the center section.
TreePlan User's Manual Page 54
Chapter 5: Building A Tree With TreePlan
******************************************************************
This chapter is a step-by-step tutorial for building the DriveTek
tree with TreePlan. Please see Chapter 2 of this manual for the
DriveTek problem and tree diagrams.
The figures in this chapter are condensed versions of what you
will see on the screen. In these figures, branch names are
abbreviated. When you build the tree, you should use more
descriptive branch names; for example, type "Prepare proposal"
instead of "Prepare".
If you make a mistake during this tutorial, you may want to save
your work before trying to fix the mistake using the destructive
Node options (Oops, Shorten, Terminal, Remove, and New); to save,
press /FS in READY mode, and enter a file name other than
"DriveTek." Also, you can always start over by using the Node New
option.
The six steps of the tutorial where you use the Node options are
numbered. The tutorial does not cover the details of entering the
branch names, partial-cash-flow values, and probabilities; simply
use the pointer keys in READY mode to move the field pointer and
begin typing or press F2 to edit.
When you run TreePlan from the DOS prompt (or when you use the
Node New option to erase a tree), the following display appears.
Terminal
Previous Branches Value
----------------- TreePlan
(None) [D]---------------|T| 0
0
The field pointer will initially be on the name field "TreePlan;"
change it to "Prepare proposal," and enter the partial-cash-flow
value -50,000. The display should appear as follows.
Terminal
Previous Branches Value
----------------- Prepare...
(None) [D]---------------|T| -50,000
-50,000
Chapter 5: Building A Tree With TreePlan Page 55
Step 1: Node Add Option
==================================================================
In READY mode, press /NA; point to the initial decision node, and
press Enter. The display should appear as follows.
+-Prepare... Terminal
Previous Branches | Value
----------------- | Decision 2
(None) [D]---------------|T| 0
0
Change the name field from "Decision 2" to "Don't prepare
proposal," and press the Up-arrow key twice. The display should
appear as follows.
Terminal
Previous Branches Value
----------------- Prepare...
(None) [D]---------------|T| -50,000
| -50,000
|
+-Don't...
Step 2: Node Event Option
==================================================================
In READY mode, press /NE2; point to the terminal node after
"Prepare proposal," and press Enter. The display should appear as
follows.
Event 3
Previous Branches +---------------|T|
----------------- Prepare... | 0 0.0
(None) [D]---------------(E)
| -50,000 | Event 4
| +---------------|T|
+-Don't... 0 0.0
TreePlan User's Manual Page 56
Change "Event 3" to "Awarded contract," and enter the
partial-cash-flow value +250,000. Also, enter the probability
0.5; TreePlan automatically changes the other probability to 0.5.
Change "Event 4" to "Not awarded contract." The display should
appear as follows.
Awarded...
Previous Branches +---------------|T|
----------------- Prepare... | +250,000 0.5
(None) [D]---------------(E)
| -50,000 | Not...
| +---------------|T|
+-Don't... 0 0.5
Step 3: Node Decision Option
==================================================================
In READY mode, press /ND3; point to the terminal node after
"Awarded contract," and press Enter. The display should appear as
follows.
Decision 5
+---------------|T|
| 0
Previous Branches |
----------------- Awarded... | Decision 6
Prepare (E)---------------[D]---------------|T|
| +250,000 0.5 | 0
| |
+-Not... | Decision 7
+---------------|T|
0
Change "Decision 5" to "Use mechanical method" with partial-cash-
flow value -120,000, change "Decision 6" to "Try electronic
method" with partial-cash-flow value -50,000, and change "Decision
7" to "Try magnetic method" with partial-cash-flow value -80,000.
The display should appear as follows.
Chapter 5: Building A Tree With TreePlan Page 57
Use mech...
+---------------|T|
| -120,000
Previous Branches |
----------------- Awarded... | Try elec...
Prepare (E)---------------[D]---------------|T|
| +250,000 0.5 | -50,000
| |
+-Not... | Try mag...
+---------------|T|
-80,000
Step 4: Node Event Option
==================================================================
In READY mode, press /NE2; point to the terminal node after "Try
electronic method," and press Enter. The display should appear as
follows.
Previous Branches +-Use mech... Event 8
----------------- | +---------------|T|
Prepare... | Try elec... | 0 0.0
Awarded... [D]---------------(E)
| -50,000 | Event 9
| +---------------|T|
+-Try mag... 0 0.0
Change "Event 8" to "Electronic success" with probability 0.5, and
change "Event 9" to "Electronic failure." The display should
appear as follows.
Previous Branches +-Use mech... Elec.success
----------------- | +---------------|T|
Prepare... | Try elec... | 0 0.5
Awarded... [D]---------------(E)
| -50,000 | Elec.failure
| +---------------|T|
+-Try mag... 0 0.5
TreePlan User's Manual Page 58
Step 5: Node Decision Option
==================================================================
In READY mode, press /ND1; point to the terminal node after
"Electronic failure," and press Enter. The display should appear
as follows.
Previous Branches
----------------- +-Elec.success
Prepare... |
Awarded... | Elec.failure Decision 10
Try elec... (E)---------------[D]---------------|T|
0 0.5 0
Change "Decision 10" to "Use mechanical method" with partial-cash-
flow value -120,000. Be sure to type this name and value the same
as the name and value on the identical branch that follows
"Awarded contract." The display should appear as follows.
Previous Branches
----------------- +-Elec.success
Prepare... |
Awarded... | Elec.failure Use mech...
Try elec... (E)---------------[D]---------------|T|
0 0.5 -120,000
Before finishing the tree, press /ZS to view a small version of
your tree so far, or press /PS, followed by Right-arrow twice, to
view the large diagram. When finished, press Escape repeatedly to
return to READY mode.
The structure of the tree (nodes and branches) following "Try
magnetic method" should be the same as the structure following
"Try electronic method," but the branch names and probabilities
are different. You could construct the remaining portion of the
tree using Node options similar to steps 4 and 5 above. An
alternative approach is to copy the structure as described below.
Step 6: Node Copy Option
==================================================================
In READY mode, press /NC. To identify the "Copy from" node, point
to the event node after "Try electronic method," and press Enter.
Then, to identify the "Copy to" node, point to the terminal node
Chapter 5: Building A Tree With TreePlan Page 59
after "Try magnetic method," and press Enter. The display should
appear as follows.
+-Use mech...
|
Previous Branches +-Try elec... Elec.success
----------------- | +---------------|T|
Prepare... | Try mag... | 0 0.5
Awarded... [D]---------------(E)
-80,000 | Elec.failure
+---------------[D]
0 0.5
On the event branches after "Try magnetic method," change
"Electronic success" to "Magnetic success" with probability 0.7,
and change "Electronic failure" to "Magnetic failure" with
probability 0.3. The display should appear as follows.
+-Use mech...
|
Previous Branches +-Try elec... Mag.success
----------------- | +---------------|T|
Prepare... | Try mag... | 0 0.7
Awarded... [D]---------------(E)
-80,000 | Mag.failure
+---------------[D]
0 0.3
The DriveTek tree is complete. You can verify your work by using
the Zoom Screen and Print Screen options.
If you press /SV in READY mode and press Home, the branch "Prepare
proposal" should be shown with double lines and certainty
equivalent +20,000.
If you press /TV in READY mode and point to the partial-cash-flow
value -120,000 under one of the branches with name "Use mechanical
method," the heading of the sensitivity analysis table should show
that there are 3 such branches.
If you save a copy of your tree, enter a file name other than
DRIVETEK. Then you will always have the original DRIVETEK.TRE
file referenced throughout this manual. (The branch names on the
DRIVETEK.TRE sample tree data file may differ slightly from those
on the tree you created.)
TreePlan User's Manual Page 60
Chapter 6: TreePlan Menu Options
******************************************************************
This chapter discusses TreePlan's menu options.
When you press the slash key in READY mode, the mode indicator in
the top right corner of the screen changes to MENU and the main
menu options are shown on the second line of the display. There
are eleven options on the main menu: Node, Solve, Print, File,
EVPI, Bayes, Table, Default, Zoom, Help, and Quit.
When a menu is being displayed, you can select the desired option
either by typing the first letter of the option or by using the
arrow keys to position the menu pointer on the option and then
pressing the Enter key. In addition, the Home and End keys move
the menu pointer to the first and last options, respectively.
The third line of the control panel either gives a brief
description of the menu option that is currently highlighted by
the menu pointer or shows the options of a submenu. For example,
if the Solve option of the main menu is highlighted, the third
line shows "Rollback to find the optimal strategy;" if the File
option is highlighted, the third line shows "Retrieve, save, or
erase a TreePlan file one disk."
Node Menu Options
==================================================================
The Node options are used to build a new decision tree model or
modify an existing tree by specifying the structure of the tree.
You can specify whether a node should be a decision node or an
event node, and you can tell TreePlan how many branches should
emanate from a node. After a Node option is completed, TreePlan
returns to READY mode, and you can enter the appropriate name,
value, and probability on each branch.
The first five Node options (Decision, Event, Add, Copy, and
Insert) increase the number of branches and nodes. Four other
Node options (Shorten, Terminal, Remove, and New) decrease the
number of branches and nodes; since these are destructive
actions, TreePlan asks for confirmation before completing the
operation.
Chapter 6: TreePlan Menu Options Page 61
Node Decision Option
------------------------------------------------------------------
Use this option to change a terminal node to a decision node with
one to five branches. In READY mode, press /ND and select the
number of decision branches desired. The mode indicator changes
to POINT, and the third line of the display shows "Point to the
terminal node to be changed to a decision node." Use the pointer
keys to move the node pointer to the appropriate terminal node,
and press the Enter key to select it. The tree display shows the
new decision node with the new decision branches, and TreePlan
returns to READY mode. Each new branch initially has value 0 and
an arbitrary name "Decision #," where the highest value of #
indicates the total number of branches in the entire tree.
Node Event Option
------------------------------------------------------------------
Use this option to change a terminal node to a event node with one
to five branches. In READY mode, press /NE and select the number
of event branches desired. The mode indicator changes to POINT,
and the third line of the display shows "Point to the terminal
node to be changed to a event node." Use the pointer keys to move
the node pointer to the appropriate terminal node, and press the
Enter key to select it. The tree display shows the new event node
with the new event branches, and TreePlan returns to READY mode.
Each new branch initially has value 0, probability 0, and an
arbitrary name "Event #," where the highest value of # indicates
the total number of branches in the entire tree.
Node Add Option
------------------------------------------------------------------
To add one more branch to an existing decision or event node,
press /NA in READY mode. The mode indicator changes to POINT, and
the third line of the display shows "Point to decision or event
node where successor branch will be added." Use the pointer keys
to move the node pointer to the appropriate node, and press the
Enter key to select it. TreePlan adds one decision or event
branch parallel to the existing branches and returns to READY
mode. The new branch initially has value 0, probability 0 (if it
is an event branch), and an arbitrary name indicating the total
number of branches in the entire tree.
TreePlan User's Manual Page 62
Node Copy Option
------------------------------------------------------------------
To copy a decision or event node with all its successors to a
terminal node, press /NC in READY mode. The mode indicator
changes to POINT, and the third line of the display shows "Point
to the decision or event node from which successors will be
copied." Use the pointer keys to move the node pointer to the
appropriate decision or event node, and press the Enter key to
select it. As you move the node pointer, the second line of the
display shows the kind of node and the number of successor
branches.
After you select the "from" node, the left portion of the second
line of the display shows the kind of node you selected and the
number of its successors, and the third line shows "Point to the
terminal node to which node and successors will be copied." As
you move the node pointer, the right portion of the second line of
the display shows the kind of node and the number of successor
branches. Use the pointer keys to move the node pointer to the
appropriate terminal node, and press the Enter key to select it.
When you select the "from" node and its successors, you are
selecting a subtree. TreePlan can append the subtree to a
terminal node, but not to a decision or event node. Also,
TreePlan cannot append the subtree to one of the subtree's own
terminal nodes.
Node Insert Option
------------------------------------------------------------------
Use this option to insert a new node and branch in the middle of a
decision tree. In READY mode, first press /NI, and then select
either Decision or Event as the kind of node and branch that will
be inserted before an existing node. For example, if you press
/NID, the mode indicator changes to POINT, and the third line of
the display shows "Point to the node before which a new decision
node and branch will be inserted." You can insert the new node
and branch in front of (to the left of) any existing decision or
event node. The new branch initially has value 0, probability 0
(if it is an event branch), and an arbitrary name indicating the
total number of branches in the entire tree.
Chapter 6: TreePlan Menu Options Page 63
Node Oops Option
------------------------------------------------------------------
To change a decision node to an event node or to change an event
node to a decision node, press /NO in READY mode. The mode
indicator changes to POINT, and the third line of the display
shows "Point to decision or event node to be changed." Use the
pointer keys to move the node pointer to the appropriate node, and
press the Enter key to select it. If you select an event node,
TreePlan asks for confirmation before deleting the probabilities.
Node Shorten Option
------------------------------------------------------------------
To shorten the tree by removing a node and its single successor
branch, press /NS in READY mode. The mode indicator changes to
POINT, and the third line of the display shows "Point to decision
or event node with single successor branch to be deleted." Use
the pointer keys to move the node pointer to the appropriate node,
and press the Enter key to select it. This option can be used
only when the branch to be deleted has no parallel branches; if
the selected node has two or more successor branches, TreePlan
displays an error message. If the selected node has a single
successor branch, TreePlan asks for confirmation before deleting
the node and branch.
If you want to delete an entire set of events or set of decisions
in the middle of a tree, first use the Node Remove option on all
but one of the branches in the set, and then use the Node Shorten
option on the single remaining node and branch. You can also use
the Node Shorten option to undo the results of the Node Insert
option.
Node Terminal Option
------------------------------------------------------------------
To change a decision or event node to a terminal node, type /NT in
READY mode. The mode indicator changes to POINT, and the third
line of the display shows "Point to the decision or event node to
be changed to a terminal node." Use the pointer keys to move the
node pointer to the appropriate node, and press the Enter key to
select it. Since this command erases all branches following the
highlighted node, TreePlan tells you how many branches will be
erased and asks for confirmation before completing the operation.
TreePlan User's Manual Page 64
Node Remove Option
------------------------------------------------------------------
To remove a node, the previous branch, and any successor nodes and
branches, type /NR in READY mode. The mode indicator changes to
POINT, and the third line of the display shows "Point to the node
following the branch to be removed." Use the pointer keys to move
the node pointer to the appropriate node, and press the Enter key
to select it. Since this command erases the highlighted node, the
previous branch, and all successor nodes and branches, TreePlan
tells you how many branches will be erased and asks for
confirmation before completing the operation.
Node New Option
------------------------------------------------------------------
To erase the entire tree, type /NN in READY mode. If the tree
hasn't been modified since the last time you saved a copy on disk,
the entire tree is erase immediately. If you have made changes to
the tree since the last time you saved it, TreePlan asks for
confirmation before erasing the tree.
Solve Menu Options
==================================================================
When you press /S in READY mode, TreePlan uses the rollback method
to find the optimal strategy. The overall solution procedure has
four steps.
(1) TreePlan checks the sum of probabilities for each set of
event branches. If a sum isn't equal to one, TreePlan
returns to READY mode with the field pointer on a probability
of the event set so that you can correct the probabilities.
If each of the sums equal one, the solution procedure
continues.
(2) For each terminal node, TreePlan determines the terminal
value by summing the partial-cash-flow values on the branches
leading from the initial node to the terminal node.
(3) The standard rollback method is used to determine a certainty
equivalent at each node. At each event node a certainty
equivalent is computed (using expected value if the decision
maker is risk neutral); at each decision node the highest
certainty equivalent of the successor nodes is selected.
Chapter 6: TreePlan Menu Options Page 65
When TreePlan uses the exponential utility function, the
absolute value of the product of the risk coefficient R times
a payoff value or certainty equivalent must be less than 88;
if not, R is too extreme relative to the value for
computational purposes, and TreePlan displays an error
message.
(4) TreePlan identifies branches associated with the optimal
strategy.
After the tree has been solved, the six Solve options are
displayed: Risk, View, Distribution, Print, Help, and Quit.
Solve Risk Options
------------------------------------------------------------------
To specify risk attitude (utility) for determining certainty
equivalents for the rollback method, select Risk from the Solve
menu, or press /SR in READY mode. The risk attitude assessment
lottery is shown on the main portion of the screen, and the risk
coefficient for the exponential utility function is shown in the
lower left corner. The six Solve Risk options are displayed:
Change, Max/Min, Neutral, Direct, Help, and Quit.
Solve Risk Change Options
------------------------------------------------------------------
To change the certainty equivalent (CE), better payoff, and worse
payoff of the risk attitude assessment lottery, select Change from
the Solve Risk menu, or press /SRC in READY mode. The four Solve
Risk Change options are displayed: CE, Better, Worse, and Quit.
Use the CE, Better, and Worse options to enter values so that the
lottery reflects the decision maker's attitude toward risk. After
a value is entered, TreePlan tries to use the lottery inputs in a
Newton-Raphson search to determine the risk coefficient parameter
R for an exponential function representing the decision maker's
risk attitude. If the attempt is successful, the value of R in
the lower left corner is updated; if R cannot be determined, the
lower left corner is blank.
When you finish entering the certainty equivalent and payoff
values, select the Quit option to use the current values to
determine R and return to the Solve menu. TreePlan checks to see
that Worse is less than CE and that CE is less than Better. Also,
if the lottery certainty equivalent is too close to one of the
TreePlan User's Manual Page 66
payoff values, the search procedure may not be able to determine
R. If the three values are not suitable, an error message is
displayed; press Escape or Enter to clear the error message, and
then enter new values.
If you press the Escape key to leave the Solve Risk menu, TreePlan
checks the values and tries to determine R. If R cannot be
determined, TreePlan reverts to the original values before you
selected the Change option. No error message is displayed.
Solve Risk Max/Min Option
------------------------------------------------------------------
To use the maximum and minimum terminal values from the decision
tree for the assessment lottery's better and worse payoffs, select
Max/Min from the Solve Risk menu, or press /SRM in READY mode.
TreePlan first searches through the terminal values to find the
highest and lowest value. The better payoff in the assessment
lottery is set equal to the maximum terminal value, and the worse
payoff is set equal to the minimum. Then TreePlan uses the
exponential utility function with the current value of the risk
coefficient R to determine the certainty equivalent for the
assessment lottery; if R is too extreme relative to the new
lottery payoffs, TreePlan changes R to zero and uses the expected
value of the new payoffs for the certainty equivalent.
Solve Risk Neutral Option
------------------------------------------------------------------
To set risk attitude for a risk neutral decision maker so that
expected values are used to determine certainty equivalents for
the rollback method, select Neutral from the Solve Risk menu, or
press /SRN in READY mode. TreePlan changes R to zero and sets the
assessment lottery certainty equivalent equal to the expected
value of the current lottery's payoffs.
Solve Risk Direct Option
------------------------------------------------------------------
To directly specify the value for the risk coefficient R of the
exponential utility function, select Direct from the Solve Risk
menu, or press /SRD in READY mode. After you enter a new risk
coefficient, TreePlan uses the exponential utility function with
the new value of R to determine the certainty equivalent for the
Chapter 6: TreePlan Menu Options Page 67
assessment lottery; if the new R is too extreme relative to the
current lottery payoffs, TreePlan changes R to zero and uses the
expected value of the payoffs for the certainty equivalent.
Solve View Option
------------------------------------------------------------------
To view the optimal strategy on the screen, select View from the
Solve menu, or press /SV in READY mode. The mode indicator
changes to VIEW, and a node is highlighted on the tree display.
Use the Page-Up, Page-Down, Home, and four arrow keys to move the
node pointer to view the entire tree. (Use Page-Up and Page-Down
to change the branch shown in detail in the center of the tree
display.) Branches associated with the optimal strategy are shown
with double lines instead of single lines, and rollback certainty
equivalents are shown to the left of each node. Partial-cash-flow
values are not shown on the solved tree. When you are finished,
press Escape or Enter to return to the Solve menu.
Solve Distribution Options
------------------------------------------------------------------
To determine the payoff distribution of the optimal strategy,
select Distribution from the Solve menu, or press /SD in READY
mode. After the distribution has been determined, the four Solve
Distribution options are displayed: Screen, Printer, File, and
Quit.
Solve Distribution Screen Option
------------------------------------------------------------------
To view the payoff distribution on the screen, select Screen from
the Solve Distribution menu, or press /SDS in READY mode. The
mode indicator changes to VIEW, and the screen shows terminal
values in ascending order with the joint probability that each
value will be obtained if the optimal strategy is followed.
Terminal values are shown using the current format value setting.
Probabilities are displayed with five decimal places; a
probability less than 0.000005 is shown as 0.00000. If the same
value is associated with two or more terminal nodes of the optimal
strategy, the sum of the joint probabilities is shown. The
expected value and standard deviation are shown at the bottom of
the payoff distribution. Use Up-arrow, Down-arrow, Page-Up, Page-
Down, Home, and End to view the entire table. When you are
TreePlan User's Manual Page 68
finished, press Escape or Enter to return to the Solve menu.
Solve Distribution Printer/File Options
------------------------------------------------------------------
To prepare to send the payoff distribution to the printer or a
print-file, select Printer or File from the Solve Distribution
menu, or press /SDP or /SDF in READY mode. The top section of the
screen shows menu options, the middle section shows applicable
current and startup settings, and the bottom section tells how
many pages will be required.
The body of the payoff distribution always has 45 characters per
line, and the number of lines equals the number of unique values
of the payoff distribution plus the seven lines for headings and
summary measures. The left margin and top margin settings
determine where the upper left corner of the payoff distribution
will appear on the output page. The bottom margin and page-length
settings determine the number of blank lines at the bottom of each
page. The number of characters on each line of the print-out or
print-file is 45 plus the current left margin, and the number of
vertical pages depends on the current settings for top margin,
bottom margin, and page length. When the settings are
satisfactory, select the Go option.
For information about the Layout, Setup, Printer, Extended (a
Printer option), and Directory options, please consult the Default
Menu Options section of this chapter.
Solve Print Options
------------------------------------------------------------------
To prepare to output the solved tree diagram, select Print from
the Solve menu, or press /SP in READY mode. The four Solve Print
options are displayed: Screen, Printer, File, and Quit.
Solve Print Screen Option
------------------------------------------------------------------
To send the solved tree diagram to the screen, select Screen from
the Solve Print menu, or press /SPS in READY mode. The mode
indicator changes to VIEW, and the solved tree is displayed. Use
the Page-Up, Page-Down, Home, End, and four arrow keys to view the
entire tree. Use the Home key to move the screen window to the
Chapter 6: TreePlan Menu Options Page 69
upper left corner of the tree diagram; if the tree is large, the
upper left corner may be blank. Use the End key to move the
screen window to the lower right corner of the tree diagram. Use
the Left-arrow or Right-arrow keys to move the screen window one
branch to the left or right. Branches associated with the optimal
strategy are shown with double lines instead of single lines, and
rollback certainty equivalents are shown to the left of each node.
Partial-cash-flow values are not shown on the solved tree. When
you are finished, press Escape or Enter to return to the Solve
Print menu.
Solve Print Printer/File Options
------------------------------------------------------------------
To prepare to send a large diagram of the solved tree to the
printer or a print-file, select Printer or File from the Solve
Print menu, or press /SPP or /SPF in READY mode. The top section
of the screen shows menu options, the middle section shows
applicable current and startup settings, and the bottom section
tells how many pages will be required. The menu options, number
of lines, number of characters per line, and number of pages are
the same for both the solved and unsolved versions of the large
diagram. For information about the large diagram, please consult
the Print Menu Options section of this chapter.
Print Menu Options
==================================================================
To prepare to output a large diagram of the unsolved tree, press
/P in READY mode. The four Print options are displayed: Screen,
Printer, File, and Quit.
Print Screen Option
------------------------------------------------------------------
To send the unsolved tree diagram to the screen, select Screen
from the Print menu, or press /PS in READY mode. The mode
indicator changes to VIEW, and the unsolved tree is displayed.
Use the Page-Up, Page-Down, Home, End, and four arrow keys to view
the entire tree. Use the Home key to move the screen window to
the upper left corner of the tree diagram; if the tree is large,
the upper left corner may be blank. Use the End key to move the
screen window to the lower right corner of the tree diagram. Use
the Left-arrow or Right-arrow keys to move the screen window one
branch to the left or right. The branch name is shown above each
TreePlan User's Manual Page 70
branch line, and the partial-cash-flow value is shown on the left
below the line; for event branches the probability is shown on
the right below the line. When you are finished, press Escape or
Enter to return to the Solve Print menu.
Print Printer/File Options
------------------------------------------------------------------
To prepare to send a large diagram of the unsolved tree to the
printer or a print-file, select Printer or File from the Print
menu, or press /PP or /PF in READY mode. The top section of the
screen shows menu options, the middle section shows applicable
current and startup settings, and the bottom section tells how
many pages will be required.
The size of the body of the large diagram, solved or unsolved,
depends on the number of terminal nodes, the number of branches on
the longest path of the tree, and the number of characters in the
largest terminal value. If T is the number of terminal nodes, the
number of lines required is 4*T - 1. If P is the number of
branches on the longest path and V is the number of characters in
the largest terminal value, the number of characters on each line
is 26*P + 3 + V.
To print a large diagram, TreePlan divides it into pages that can
be joined together after printing. The number of horizontal pages
depends on the current settings for left margin and right margin,
and the number of vertical pages depends on the current settings
for top margin, bottom margin, and page length. If you adjust the
current layout settings, TreePlan updates the bottom of the
display showing the number of pages required. When the settings
are satisfactory, select the Go option.
For information about the Format, Layout, Setup, Printer, Extended
(a Printer option), and Directory options, please consult the
Default Menu Options section of this chapter.
File Menu Options
==================================================================
To manage files created by TreePlan, press /F in READY mode. Six
File options are displayed: Retrieve, Save, Erase, List,
Directory, and Help.
TreePlan works with two kinds of files: tree data files
(identified by a .TRE extension) and print-files (.PRN extension).
Chapter 6: TreePlan Menu Options Page 71
Use the Retrieve and Save options to read and write tree data
files, which are standard ASCII text files containing branch/node
data: node ID number, branch name, partial-cash-flow value,
probability, predecessor ID, kind of node, number of successors,
and successor IDs. Use various print options to create
print-files containing line-oriented tables and diagrams,
identical to output that is sent to a printer; these print-files
are standard ASCII text files.
The File options affect tree data files and print files only in
the current directory. Use the Directory option to access files
in other directories.
File Retrieve Option
------------------------------------------------------------------
To read a tree data file from disk, select Retrieve from the File
menu, or press /FR in READY mode. This command replaces the tree
in memory with a copy of a tree from a data file on disk. If you
have made changes to the tree in memory since the last time you
saved it, TreePlan asks for confirmation. The mode indicator
changes to POINT, and the display shows a list of tree data files
in the current directory. Point to the desired filename, and
press Enter to select. TreePlan erases the tree in memory, loads
a copy of the tree from the data file, and returns to READY mode.
File Save Option
------------------------------------------------------------------
To store a copy of the tree in memory in a tree data file on disk,
select Save from the File menu, or press /FS in READY mode. The
display shows a list of tree data files in the current directory,
and the mode indicator changes to INSERT. Type a file name at the
prompt on the second line. Do not use an extension in the
filename you type; TreePlan adds the .TRE extension
automatically. File names can be up to eight characters long and
can include upper-case and lower-case letters, numbers, and the
underscore character (_). TreePlan does not accept a period or
space character in a file name. If you type a filename that
already exists, TreePlan asks for confirmation before it erases
the existing file and creates a new tree data file with the same
name. After the tree is saved on disk, TreePlan returns to READY
mode.
TreePlan User's Manual Page 72
File Erase Tree/Print Options
------------------------------------------------------------------
To erase a tree data file or print-file on disk, select Erase from
the File menu and then select Tree or Print. Alternatively, press
/FET or /FEP in READY mode. The display shows a list of tree data
files (.TRE extension) or print-files (.PRN extension) in the
current directory, and the mode indicator changes to POINT. Use
the pointer keys to move the pointer to the appropriate filename,
and press Enter to select it. TreePlan does not ask for
confirmation; the file you select is erased immediately. Before
selecting a file, press Escape to return to the previous menu
without erasing a file.
File List Tree/Print Options
------------------------------------------------------------------
To display the names of tree data files or print-files on disk,
select List from the File menu and then select Tree or Print.
Alternatively, press /FLT or /FLP in READY mode. The display
shows a list of tree data files (.TRE extension) or print-files
(.PRN extension) in the current directory, and the mode indicator
changes to VIEW. When finished, press Enter to return to the File
menu, or press Escape to return to the File List menu.
File Directory Option
------------------------------------------------------------------
To enter the name of a different disk directory for tree data
files and print-files, select Directory from the File menu, or
press /FD in READY mode. The mode indicator changes to INSERT
with the cursor at the end of the current directory name on the
second line. Edit the directory name; press Enter when finished,
or press Escape to return to the File menu without changing the
current directory. For additional information about using
directories, please see the Default Menu Options section of this
chapter.
EVPI Menu Options
==================================================================
To compute Expected Value of Perfect Information (EVPI), press /E
in READY mode. The mode indicator changes to POINT, and the third
line of the display shows "Point to event node preceding event set
Chapter 6: TreePlan Menu Options Page 73
for EVPI computation." Use the pointer keys to move the node
pointer to the appropriate event node, and press the Enter key to
select it.
After you select an event set for EVPI, TreePlan temporarily
expands your decision tree as follows.
(1) A decision branch "No additional info" is inserted at the
initial node in front of your original decision tree.
(2) A second decision branch "Use perfect prediction" is added to
the initial node.
(3) "Use perfect prediction" is followed by a copy of the event
set you selected with the branch names shown in quotes on the
expanded tree.
(4) A copy of your original decision tree follows each of the
perfect prediction event branches. TreePlan automatically
assigns conditional probabilities of zero and one to
appropriate events.
TreePlan solves the expanded tree using the rollback method with
expected values, displays the solved tree with the "Use perfect
prediction" branch in the center of the display, and shows EVPI in
the lower left corner of the screen. EVPI is the difference
between the expected value of the best strategy with no additional
information (your original problem) and the expected value of the
best strategy using a perfect prediction.
After the expanded tree has been solved, the mode indicator
changes to MENU and the four EVPI options are displayed: View,
Retain, Help, and Quit.
EVPI View Option
------------------------------------------------------------------
To view the solved expanded tree, select View from the EVPI menu,
or press /EV in READY mode. The mode indicator changes to VIEW,
and a node is highlighted on the tree display. Use the Page-Up,
Page-Down, Home, and four arrow keys to move the node pointer to
view the entire tree. (Use Page-Up and Page-Down to change the
branch shown in detail in the center of the tree display.)
Branches associated with the optimal strategy are shown with
double lines instead of single lines, and rollback certainty
equivalents are shown to the left of each node. Partial-cash-flow
values are not shown on the solved tree. When you are finished,
press Escape or Enter to return to the EVPI menu.
TreePlan User's Manual Page 74
EVPI Retain Option
------------------------------------------------------------------
To return to READY mode with the expanded EVPI tree, select Retain
from the EVPI menu, or press /ER in READY mode. For example, use
this option if you want to modify the expanded tree, print the
expanded tree diagram, or solve the expanded tree using an
exponential utility function to determine value of information.
To return to READY mode with only the original tree, select Quit
from the EVPI menu or press Escape.
Bayes Menu Options
==================================================================
To perform Bayesian revision of probabilities, first use the Node
options to build a decision tree containing the main events that
directly affect the payoffs and the information events that are
the results of the information-gathering effort.
After you have a tree with the main events and information events,
press /B in READY mode to perform Bayesian revision. Eight Bayes
options are displayed: Link, Input, Screen, Printer, File,
Transfer, Help, and Quit.
You must use the Link Main-event and Link Info-event options
before using the Input, Screen, Printer, File, and Transfer
options. If you use the Link options, return to READY mode, and
make any modifications to the tree, you must use the Link options
again before using the other five options.
Bayes Link Options
------------------------------------------------------------------
To identify the main events and information events on the decision
tree for Bayesian revision, select Link from the Bayes menu, or
press /BL in READY mode. Two Bayes Link options are displayed:
Main-event and Info-event.
To identify the main events on the decision tree for Bayesian
revision, select Main-event from the Bayes Link options. Then
point to a node that precedes the main events, and press Enter to
select it. The main event branches usually appear at several
places on the decision tree. One set of main events usually has
Chapter 6: TreePlan Menu Options Page 75
prior probabilities, and other sets of main events will have
posterior probabilities after Bayesian revision. The branch names
must be identical for each set of main events.
To identify the information events on the decision tree for
Bayesian revision, select Info-event from the Bayes Link options.
Then point to the node that precedes the information events, and
press Enter to select it. The information event branches usually
appear at only one place on the decision tree. The set of
information events will have preposterior probabilities after
Bayesian revision.
Bayes Input Options
------------------------------------------------------------------
After you select the main event and information event nodes, to
specify input probabilities for Bayesian revision, select Input
from the Bayes options, or press /BI in READY mode. Two Bayes
Input options are displayed: Prior/Likelihood and Joint.
To change the prior and likelihood input probabilities for
Bayesian revision, select Prior/Likelihood from the Bayes Input
options, or press /BIP in READY mode. The mode indicator changes
to BAYES, and a probability tree shows the main events with prior
probabilities on the left and information events with likelihood
probabilities on the right. Use the pointer keys to move the
highlighted field pointer among the prior and likelihood
probabilities.
To change the joint probabilities for Bayesian revision, select
Joint from the Bayes Input options, or press /BIJ in READY mode.
The mode indicator changes to BAYES, and a probability tree shows
the main events on the left, information events in the center, and
joint probabilities on the right. Use the pointer keys to move
the highlighted field pointer among the joint probabilities.
In BAYES mode, press F2 to edit a probability, or simply start
typing to replace the contents of a field with a new probability.
While editing a probability, press the Insert key to toggle
between INSERT and OVERTYPE modes; press Escape to restore the
original probability; press Enter to have TreePlan accept the new
probability. When you finish modifying the input probabilities
and want to leave the BAYES input mode, press Enter to return to
the Bayes menu, or press Escape to return to the Bayes Input
options.
After you use the Bayes Link options to select the main event and
information event nodes, the initial joint probabilities for the
TreePlan User's Manual Page 76
two event sets are computed assuming statistical independence.
The prior probabilities on the main event branches may be correct,
but usually you will have to modify the likelihood or joint
probabilities to reflect the correct inputs for Bayesian revision.
Bayes Screen Option
------------------------------------------------------------------
After you select the main event and information event nodes, to
view all Bayesian probabilities, select Screen from the Bayes
options, or press /BS in READY mode. The top probability tree
shows inputs (priors and likelihoods) and joint probabilities;
the bottom probability tree shows outputs (preposteriors and
posteriors) and joint probabilities. All probabilities are shown
using five decimal places. Use Up-arrow, Down-arrow, Page-up,
Page-down, Home, and End keys to view the probability trees. When
finished, press Enter or Escape to return to the Bayes menu.
Bayes Printer/File Options
------------------------------------------------------------------
After you select the main event and information event nodes, to
prepare to send the Bayes probability trees to the printer or a
print-file, select Printer or File from the Bayes menu, or press
/BP or /BF in READY mode. The top section of the screen shows
menu options, the middle section shows applicable current and
startup settings, and the bottom section tells how many pages will
be required.
The body of the output of the Bayes probability trees always has
78 characters per line, and the number of lines depends on
the number of branches plus headings. If M is the number of
branches for the main events and I is the number of branches for
the information events, the number of lines required is 6 + 6*M*I.
The left margin and top margin settings determine where the upper
left corner of the top heading will appear on the output page.
The bottom margin and page-length settings determine the number of
blank lines at the bottom of each page. The number of characters
on each line of the print-out or print-file is 78 plus the current
left margin, and the number of vertical pages depends on the
current settings for top margin, bottom margin, and page length.
When the settings are satisfactory, select Go from the menu.
For information about the Layout, Setup, Printer, Extended (a
Printer option), and Directory options, please consult the Default
Chapter 6: TreePlan Menu Options Page 77
Menu Options section of this chapter.
Bayes Transfer Options
------------------------------------------------------------------
After you select the main event and information event nodes, to
prepare to transfer the Bayesian probabilities to the decision
tree, select Transfer from the Bayes menu, or press /BT in READY
mode. Since existing probabilities will be modified, TreePlan
asks for confirmation before completing the operation. This
option changes the probability on every branch of the decision
tree with a name identical to the main event and information event
branches.
If a main event branch on the decision tree is preceded by an
information event branch, a posterior probability P(Main | Info)
is assigned; if a main event branch has no such predecessor, a
prior probability P(Main) is assigned. Likelihood probabilities
do not normally appear on a decision tree, but if an information
event branch on the decision tree is preceded by a main event
branch, a likelihood probability P(Info | Main) is assigned; if
an information event branch has no such predecessor, a
preposterior probability P(Info) is assigned.
Table Value Menu Options
==================================================================
To create a table for sensitivity analysis of a partial-cash-flow
value, press /TV in READY mode. The mode indicator changes to
POINT, and the third line of the display shows "Point to value for
sensitivity analysis." Use the pointer keys to move the field
pointer to the value of interest, and press the Enter key to
select it. After you select the base-case value, the mode
indicator changes to MENU, and the six Table Value options are
displayed: Load, View, Printer, File, Help, and Quit. TreePlan
also displays the heading of the table, showing the value you
selected, the branch name, the risk coefficient R, and the number
of branches that have the same name and value.
Table Value Load Option
------------------------------------------------------------------
To load a set of temporary values into the table by specifying
start, step, and stop values, select Load from the Table Value
TreePlan User's Manual Page 78
menu. You can use a positive or negative step value to fill the
table with values in ascending or descending order. The table
holds a maximum of thirteen temporary values. After you specify
the start, step, and stop values, TreePlan determines each
temporary partial-cash-flow value, temporarily changes the value
on all branches having the same name and base-case value, solves
the tree using the rollback method, and displays the results in a
table. Each row of the table shows results for a case that can be
compared to the base case. The table shows each temporary value,
the certainty equivalent of the optimal strategy when that
temporary value is used, and whether the optimal strategy using
the temporary value is the same as the optimal strategy using the
base-case value. After the results are displayed, the mode
indicator changes from WAIT to MENU, and you can select other
Table Value options.
Table Value View Option
------------------------------------------------------------------
To view the optimal strategy for a case, select View from the
Table Value menu. The mode indicator changes to POINT, and an
entire row of the table is highlighted. Use the pointer keys to
highlight a case of interest, and press Enter to select it. The
mode indicator changes to VIEW, and the solved tree using the
temporary values for the selected case is displayed. Use the
pointer keys to view the solved tree; when finished, press Enter
or Escape to return to the table with the highlighted row in POINT
mode. Select another case, or press Escape to return to the Table
Value menu.
Table Value Printer/File Options
------------------------------------------------------------------
To prepare to send the value sensitivity analysis table to the
printer or a print-file, select Printer or File from the Table
Value menu. The top section of the screen shows menu options, the
middle section shows applicable current and startup settings, and
the bottom section tells how many pages will be required.
The body of the table always has 55 characters per line, and the
number of lines equals the number of temporary values (a maximum
of thirteen cases) plus six lines for the table heading. The left
margin and top margin settings determine where the upper left
corner of the table will appear on the output page. The bottom
margin and page-length settings determine the number of blank
lines at the bottom of each page. The number of characters on
Chapter 6: TreePlan Menu Options Page 79
each line of the print-out or print-file is 55 plus the current
left margin. Values and certainty equivalents are always shown
using two decimal places, and the table is always a single page.
When the settings are satisfactory, select Go from the menu.
For information about the Layout, Setup, Printer, Extended (a
Printer option), and Directory options, please consult the Default
Menu Options section of this chapter.
Table Probability Menu Options
==================================================================
To create a table for sensitivity analysis of a probability, press
/TP in READY mode. The mode indicator changes to POINT, and the
third line of the display shows "Point to probability for
sensitivity analysis." Use the pointer keys to move the field
pointer to the value of interest, and press the Enter key to
select it. After you select the base-case probability, the mode
indicator changes to MENU, and the seven Table Probability options
are displayed: Load, Tenths, View, Printer, File, Help, and Quit.
TreePlan also displays the heading of the table, showing the
probability you selected, the branch name, the risk coefficient R,
and the number of identical event sets. Event sets are identical
if the branches following an event node have the same branch names
and the same base-case probabilities.
Table Probability Load Option
------------------------------------------------------------------
To load a set of temporary probabilities into the table by
specifying start, step, and stop values, select Load from the
Table Probability menu. TreePlan accepts only a positive step
value, so the table will be filled with probabilities in ascending
order. The table holds a maximum of thirteen temporary values.
After you specify the start, step, and stop values, TreePlan
determines each temporary probability, temporarily changes the
probabilities on identical event sets, solves the tree using the
rollback method, and displays the results in a table. Each row of
the table shows results for a case that can be compared to the
base case. The table shows each temporary probability, the
certainty equivalent of the optimal strategy when that temporary
probability is used, and whether the optimal strategy using the
temporary probability is the same as the optimal strategy using
the base-case probability. Probabilities are always shown using
five decimal places. After the results are displayed, the mode
indicator changes from WAIT to MENU, and you can select other
TreePlan User's Manual Page 80
Table Probability options.
When the base-case probability is changed, probabilities on other
branches in the event set are changed so that they retain the same
proportional relationship as the base case. For example, assume
events Low, Medium, High have probabilities 0.1, 0.3, and 0.6,
respectively. If you select probability of Low, 0.1, for
sensitivity analysis, the probabilities for Medium and High will
have the ratio 0.3 to 0.6 for each case you analyze. If the
probability of Low is changed temporarily to 0.2, the remaining
0.8 probability will be allocated according to the base-case
ratio, so the temporary probabilities for Medium and High will be
0.26667 and 0.53333.
Table Probability Tenths Option
------------------------------------------------------------------
To load the table with temporary probabilities 0.0, 0.1, ..., 1.0,
select Tenths from the Table Probability menu. The results are
the same as using the Load option with start = 0.0, step = 0.1,
and stop = 1.0.
Table Probability View Option
------------------------------------------------------------------
The View option of the Table Probability menu works the same as
that of the Table Value menu. For information, please consult the
Table Value View Option section of this chapter.
Table Probability Printer/File Options
------------------------------------------------------------------
The Printer and File options of the Table Probability menu work
the same as those of the Table Value menu. For information,
please consult the Table Value Printer/File Options section of
this chapter.
Table Lottery-CE Menu Options
==================================================================
If you want to characterize attitude toward risk using the
certainty equivalent (CE) of the assessment lottery, first specify
Chapter 6: TreePlan Menu Options Page 81
the base-case values for sensitivity analysis. In READY mode,
press /SRC, and use the Solve Risk Change options to specify the
better payoff, worse payoff, and certainty equivalent for the
assessment lottery.
After specifying the base case, to create a table for sensitivity
analysis of the lottery certainty equivalent, press /TL in READY
mode. The mode indicator changes to MENU and the six Table
Lottery-CE options are displayed: Load, View, Printer, File,
Help, and Quit. TreePlan also displays the heading of the table,
showing the base-case lottery certainty equivalent, the base-case
risk coefficient R, and the assessment lottery's better and worse
payoffs, which apply to all cases that will be shown in the
table.
Table Lottery-CE Load Option
------------------------------------------------------------------
To load a set of temporary lottery certainty equivalents into the
table by specifying start, step, and stop values, select Load from
the Table Lottery-CE menu. You can use a positive or negative
step value to fill the table with certainty equivalents in
ascending or descending order. The table holds a maximum of
thirteen temporary certainty equivalents. After you specify the
start, step, and stop values, TreePlan determines each temporary
certainty equivalent, finds the associated risk coefficient R,
solves the tree using the rollback method with the exponential
utility function, and displays the results in a table. Each row
of the table shows results for a case that can be compared to the
base case; the better payoff and worse payoff of the assessment
lottery are the same for each case. The table shows each
temporary certainty equivalent of the assessment lottery, the
associated risk coefficient R, the certainty equivalent of the
optimal strategy when that risk coefficient is used in the
exponential utility function, and whether the optimal strategy
using the temporary risk coefficient is the same as the optimal
strategy using the base risk coefficient. After the results are
displayed, the mode indicator changes from WAIT to MENU, and you
can select other Table Lottery-CE options.
Table Lottery-CE View Option
------------------------------------------------------------------
The View option of the Table Lottery-CE menu works the same as
that of the Table Value menu. For information, please consult the
Table Value View Option section of this chapter.
TreePlan User's Manual Page 82
Table Lottery-CE Printer/File Options
------------------------------------------------------------------
The Printer and File options of the Table Lottery-CE menu work the
same as those of the Table Value menu, except that the body of the
table has 75 characters per line instead of 55. For information,
please consult the Table Value Printer/File Options section of
this chapter.
Table Risk-Coefficient Menu Options
==================================================================
If you want to characterize attitude toward risk using the risk
coefficient directly, first specify the base-case risk coefficient
for sensitivity analysis. In READY mode, press /SRD (Solve Risk
Direct) and enter the base-case risk coefficient.
If you also want to interpret the associated certainty equivalents
of the assessment lottery, press /SRC in READY mode, and use the
Solve Risk Change options to specify the better and worse payoffs
of the assessment lottery.
After specifying the base case, to create a table for sensitivity
analysis of the risk coefficient, press /TR in READY mode. The
mode indicator changes to MENU and the six Table Risk-Coefficient
options are displayed: Load, View, Printer, File, Help, and Quit.
TreePlan also displays the heading of the table, showing the base-
case lottery certainty equivalent, the base-case risk coefficient
R, and the assessment lottery's better and worse payoffs, which
apply to all cases that will be shown in the table.
Table Risk-Coefficient Load Option
------------------------------------------------------------------
To load a set of temporary risk coefficients into the table by
specifying start, step, and stop values, select Load from the
Table Risk-Coefficient menu. You can use a positive or negative
step value to fill the table with risk coefficients in ascending
or descending order. The table holds a maximum of thirteen
temporary risk coefficients. After you specify the start, step,
and stop values, TreePlan determines each temporary risk
coefficient, finds the associated certainty equivalent for the
assessment lottery, solves the tree using the rollback method with
Chapter 6: TreePlan Menu Options Page 83
the exponential utility function, and displays the results in a
table. Each row of the table shows results for a case that can be
compared to the base case; the better payoff and worse payoff of
the assessment lottery are the same for each case. The table
shows each temporary risk coefficient R, the associated certainty
equivalent of the assessment lottery, the certainty equivalent of
the optimal strategy when the temporary risk coefficient is used
in the exponential utility function, and whether the optimal
strategy using the temporary risk coefficient is the same as the
optimal strategy using the base risk coefficient. After the
results are displayed, the mode indicator changes from WAIT to
MENU, and you can select other Table Risk-Coefficient options.
Table Risk-Coefficient View Option
------------------------------------------------------------------
The View option of the Table Risk-Coefficient menu works the same
as that of the Table Value menu. For information, please consult
the Table Value View Option section of this chapter.
Table Risk-Coefficient Printer/File Options
------------------------------------------------------------------
The Printer and File options of the Table Risk-Coefficient menu
work the same as those of the Table Value menu, except that the
body of the table has 75 characters per line instead of 55. For
information, please consult the Table Value Printer/File Options
section of this chapter.
Default Menu Options
==================================================================
To verify or set TreePlan's global settings, press /D in READY
mode. Nine Default options are displayed: Format, Layout, Setup,
Printer, Directory, Clear, Update, Help, and Quit.
There are two sets of default settings: current and startup. The
current settings are those in effect when you are using TreePlan.
You can change the current settings from the Default menu and from
various printer and print-file menus.
The startup settings are the settings used by TreePlan when you
start the program from the DOS prompt. Initially, TreePlan looks
for the configuration file (TREEPLAN.CFG) containing the settings.
TreePlan User's Manual Page 84
If the file is found, the startup settings are set equal to those
stored in the configuration file. If TreePlan can't find the file
or has a problem reading the file, TreePlan sets the startup
settings equal to settings that are a permanent part of the
TreePlan program. After the startup settings have been
determined, TreePlan sets the current settings equal to the
startup settings.
If you run TreePlan from the A: drive without a configuration file
and press /D in READY mode, you will see the following settings.
Current Startup
Setting Setting
------- -------
Format + Value decimal places 0 0
+ Probability decimal places 3 3
Layout + Left margin 0 0
| Right margin 80 80
| Top margin 0 0
| Bottom margin 0 0
+ Page-Length 66 66
Setup string for printer (None) (None)
Printer + Interface LPT1 LPT1
| Extended characters No No
| Automatic Line Feed No No
+ Paper continuous feed Yes Yes
Directory for files A:\ (None)
The startup settings shown above are TreePlan's built-in settings;
the current settings are the same, except for the directory for
files, which TreePlan has set to the drive/directory where you
started the program.
Default Format Options
------------------------------------------------------------------
To select decimal places for value and probability formats, select
Format from the Default menu or from various print-printer and
print-file menus. The format options determine how values
(partial-cash-flows, certainty equivalents, and terminal values)
and probabilities will be formatted for display when viewing or
printing the large tree diagram.
The number of decimal places for values can be zero (integer) or
two (dollars and cents), and the number of decimal places for
probabilities can be two, three, four, or five. Some program
Chapter 6: TreePlan Menu Options Page 85
options override the format settings; for example, probabilities
of a payoff distribution are always shown with five decimal
places.
Default Layout Options
------------------------------------------------------------------
To enter margins and page length for printer and print-file
output, select Layout from the Default menu or from various print-
printer and print-file menus. The layout options determine how
output will be placed on a page; these settings apply to both
printer and print-file output.
The left margin setting specifies the number of space characters
(blanks) that TreePlan sends to the printer at the start of each
line on a page. The left margin must be between 0 and 40.
The right margin setting specifies the total number of characters
on each line that TreePlan sends to the printer. The right margin
must be between 41 and 240. Some program options override this
setting; for example, Bayes probability output always sends the
current left margin plus 78 characters. If you set the right
margin too high, TreePlan may send more characters per line than
your printer can accept; in this case, your printer may lose the
extra characters or print them on the next line, sometimes with
unpredictable results. Some printers can be set to print in a
condensed or compressed mode, in which case the printer will be
able to accept more characters per line.
The top margin setting specifies the number of blank lines at the
top of each page of output. The top margin must be between 0 and
10.
The bottom margin setting specifies the number of blank lines at
the bottom of each page. The bottom margin must be between 0 and
10.
The page length setting specifies the total number of lines on
each page that TreePlan sends to the printer. The page length
must be between 21 and 999. Some of these lines, including the
top and bottom margins, may be blank. Most printers print six
lines per inch, so standard 11-inch paper will have 66 lines per
page. Some printers can be set to print eight lines per inch, in
which case you could set the page length to 88.
TreePlan User's Manual Page 86
Default Setup Option
------------------------------------------------------------------
To enter a setup string for the printer, select Setup from the
Default menu or from various print-printer menus. A setup string
is a string of characters sent to the printer to activate specific
printer functions (e.g., compressed print). Refer to your printer
manual for the appropriate setup string characters, translate each
character into its three-digit numerical ASCII code, and precede
each three-digit code with a backslash when specifying the setup
string.
For example, \015 sends a special character that tells most IBM
and Epson printers to use condensed print, approximately 16.67
characters per inch. In this case, you may be able to print
approximately 140 characters per line on standard 8.5-inch paper
by using a setup string and adjusting the layout right margin
setting.
Since special characters may cause unpredictable results in ASCII
text files, TreePlan disregards the setup string when sending
output to a print-file.
Default Printer Options
------------------------------------------------------------------
To select printer hardware settings, select Printer from the
Default menu or from various print-printer menus. There are four
options: Interface, Extended, Auto-LF, and Paper. (The Extended
option is also available from various print-file menus.) These
settings specify hardware characteristics of your printer and its
interface.
The interface setting specifies the printer port: LPT1, LPT2,
LPT3, COM1, or COM2. A typical system uses LPT1, sometimes called
PRN. If you plan to use COM1 or COM2 for a serial printer, first
use the DOS MODE command to specify baud rate, parity, and stop
bits before running TreePlan.
The extended characters setting specifies whether the printer can
print the line drawing characters of the IBM extended character
set. If not, TreePlan sends only standard ASCII characters to the
printer or print-file.
The automatic line feed setting specifies whether the printer
performs an automatic line feed after each carriage return. If
so, TreePlan ends each line with only a carriage return; if not,
TreePlan ends each line with a carriage return and a line feed.
Chapter 6: TreePlan Menu Options Page 87
If your printer is overprinting your output on a single line or
double-spacing between lines, change this setting. This setting
does not affect lines sent to a print-file, which always end with
a carriage return and line feed.
The paper continuous feed setting specifies whether the printer
uses continuous-feed paper. If not, TreePlan pauses after each
page of a multi-page print-out so you can change single sheets
before resuming printing. This setting does not affect print-file
output.
Default Directory Option
------------------------------------------------------------------
To enter the name of a directory for tree data files and print-
files, select Directory from the Default menu, the File menu, or
various print-file menus. TreePlan uses the current directory for
saving and retrieving tree data files and for writing print-files
to disk.
When you run the program by typing TreePlan at the DOS prompt,
TreePlan looks for its configuration file in the initial
directory. If TreePlan can't find the configuration file, it uses
the disk drive and/or directory you ran the program from (the load
directory) as the current directory. If the configuration file is
found, TreePlan reads it, uses the configuration settings, and
checks to see whether the directory specified in the file exists.
If the directory exists, TreePlan uses it as the current
directory. If TreePlan can't access the directory specified in
the configuration file, Treeplan shows an error message. After
you press Escape or Enter to clear the error message, TreePlan
uses the load directory as the current directory. In this case,
the directory specified in the configuration file is shown as the
startup directory, even though it may not exist.
The Directory option does not create a directory; it only allows
TreePlan to make use of files in a directory that already exists.
Before running TreePlan, use the DOS command MkDir (or MD) to
create a directory.
Default Clear Option
------------------------------------------------------------------
To erase all current settings and establish new current settings
equal to the startup settings, select Clear from the Default menu
or from various print-printer and print-file menus.
TreePlan User's Manual Page 88
Default Update Option
------------------------------------------------------------------
To save the current settings as new startup settings in a
configuration file (TREEPLAN.CFG), select Update from the Default
menu.
The original TreePlan disk does not have a configuration file. If
the built-in values are appropriate for your computer system and
printer, you may continue to use the program without ever creating
a configuration file. On the other hand, if you want to customize
the settings and retain the new values so that they are used
automatically each time you start the program, use this option.
If you run TreePlan from a floppy disk, be sure that the disk
containing the TreePlan program file TREEPLAN.EXE is in the drive
before you execute the Update command. Also, be sure that the
floppy disk is not write-protected; remove the write-protect tab
on a 5.25-inch disk; close the write-protect window on a 3.5-inch
disk.
Zoom Menu Options
==================================================================
To prepare to output a small diagram of the unsolved tree, press
/Z in READY mode. The four Zoom options are displayed: Screen,
Printer, File, and Quit. You may want to use this option to view
the overall structure of a large tree.
Zoom Screen Option
------------------------------------------------------------------
To send a small diagram of the unsolved tree to the screen, select
Screen from the Zoom menu, or press /ZS in READY mode. The mode
indicator changes to VIEW, and a small diagram of the unsolved
tree is displayed. Branch names are shortened by eliminating
spaces and vowels or by truncating the name; probabilities,
partial-cash-flow values, and terminal values are not shown. Use
the Page-Up, Page-Down, Home, End, and four arrow keys to view the
entire tree. Use the Home key to move the screen window to the
upper left corner of the tree diagram. Use the End key to move
the screen window to the lower right corner of the tree diagram.
Use the Left-arrow or Right-arrow keys to move the screen window
Chapter 6: TreePlan Menu Options Page 89
one branch to the left or right. When you are finished, press
Escape or Enter to return to the Zoom menu.
Zoom Printer/File Options
------------------------------------------------------------------
To prepare to send a small diagram of the unsolved tree to the
printer or a print-file, select Printer or File from the Zoom
menu, or press /ZP or /ZF in READY mode. The top section of the
screen shows menu options, the middle section shows applicable
current and startup settings, and the bottom section tells how
many pages will be required.
The size of the body of the small diagram of the unsolved tree
depends on the number of terminal nodes and the number of branches
on the longest path of the tree. If T is the number of terminal
nodes, the number of lines required is 2*T - 1. If P is the
number of branches on the longest path, the number of characters
on each line is 13*P + 2.
To print the small diagram, TreePlan divides it into pages that
can be joined together after printing. The number of horizontal
pages depends on the current settings for left margin and right
margin, and the number of vertical pages depends on the current
settings for top margin, bottom margin, and page length. If you
adjust the current layout settings, TreePlan updates the bottom of
the display showing the number of pages required.
For information about the Layout, Setup, Printer, Extended (a
Printer option), and Directory options, please consult the Default
Menu Options section of this chapter.
An example of Zoom output is included in the Valley Problem (B)
section of Chapter 3.
TreePlan User's Manual Page 90
Appendix A: References
******************************************************************
This first four books listed below were specifically referenced
in this User's Manual. There are many other books and articles
on decision analysis, and decision trees in particular, that you
might want to investigate.
Bierman, Harold, Jr., Charles P. Bonini, and Warren H. Hausman,
_Quantitative Analysis for Business Decisions_, Eighth
Edition, Homewood, IL: Richard D. Irwin, Inc., 1991.
Holloway, Charles A., _Decision Making Under Uncertainty: Models
and Choices_, Englewood Cliffs, NJ: Prentice-Hall, Inc.,
1979.
McNamee, Peter, and John Celona, _Decision Analysis for the
Professional with Supertree_, Redwood City, CA: The
Scientific Press, 1987.
Spurr, William A., and Charles P. Bonini, _Statistical Analysis for
Business Decisions_, Revised Edition, Homewood, IL: Richard
D. Irwin, Inc., 1973.
The following book is highly recommended for its practical examples
and complete coverage of all techniques used in modern decision
decision analysis, including influence diagrams, decision trees,
and Monte Carlo simulation.
Clemen, Robert T., _Making Hard Decisions: An Introduction to
Decision Analysis_, Boston, MA: PWS-Kent, 1991.
Appendix A: References Page 91
Appendix B: TreePlan Error Messages
******************************************************************
This appendix lists error messages that may appear on the bottom
line of the screen as you work with TreePlan. Messages are listed
alphabetically. Pressing Escape or Enter clears the error message
from the screen but does not correct the problem.
Base probability cannot be 1.0: The probability you select for
sensitivity analysis cannot be 1.0. (Table Probability
Options)
Can copy only to a terminal node (Node Copy Option)
Cannot copy from a terminal node (Node Copy Option)
Cannot copy from the initial node (Node Copy Option)
Cannot copy to a successor of the "copy from" node (Node Copy
Option)
Cannot create file: Be sure to enter a valid file name.
Cannot open file: The file you specified either doesn't exist or
is in a different disk or directory.
Cannot read tree data file from disk: The file is probably
corrupted.
Cannot write file to disk: The disk you are trying to write to is
full, or there are too many entries in the directory. Press
the Escape key repeatedly to return to READY mode; change
the disk or erase unneeded files; retry the option.
Certainty equivalent too close to lottery payoff value: With the
current inputs, TreePlan cannot determine the risk
coefficient for an exponential utility function. Try a
certainty equivalent closer to the expected value of the risk
attitude assessment lottery. (Solve Risk Options)
Directory does not exist: Make sure you type the exact path name
of the directory.
Disk drive not ready: The disk drive specified in the directory
setting is not ready for input and output. Make sure you
have fully inserted a disk in the proper floppy drive; on a
5.25-inch drive make sure the drive door or lever is closed.
TreePlan User's Manual Page 92
Disk is write-protected: If you want to erase a file or write a
file to disk, remove the write-protect tab on a 5.25-inch
disk or close the write-protect window on a 3.5-inch disk.
Each temporary certainty equivalent must be greater than worse
payoff: Use the Load option to enter appropriate stop and
start values. (Table Lottery-CE Load Option)
Each temporary certainty equivalent must be less than better
payoff: Use the Load option to enter appropriate stop and
start values. (Table Lottery-CE Load Option)
Enter Worse < CE and CE < Better: The three values you specify
for the risk attitude assessment lottery must be chosen so
that the worse payoff is strictly less than the certainty
equivalent and the certainty equivalent is strictly less than
the better payoff. (Solve Risk Change Options)
Event probability for EVPI cannot be 1: The event node you select
cannot have a branch with probability 1. (EVPI Menu Options)
Info-event node must have at least two successor branches (Bayes
Link Options)
Initial node must be decision node with at least one branch: You
cannot change or eliminate the initial decision node.
Link to info-event first: Although you have selected a main-event
node, you must also select an info-event node before trying
to use the Input, Screen, Printer, File, or Transfer options
of the Bayes menu.
Link to main-event and info-event first: You must select both a
main-event node and an info-event node before trying to use
the Input, Screen, Printer, File, or Transfer options of the
Bayes menu.
Link to main-event first: Although you have selected an info-
event node, you must also select a main-event node before
trying to use the Input, Screen, Printer, File, or Transfer
options of the Bayes menu.
Load table first: You must use the Load option before trying to
use the View, Printer, or File options of a sensitivity
analysis table.
Main-event node and info-event node cannot be the same (Bayes
Link Options)
Appendix B: TreePlan Error Messages Page 93
Main-event node must have at least two successor branches (Bayes
Link Options)
Maximum and minimum terminal values must be farther apart (Solve
Risk Max/Min Option)
Maximum number of successors is five (Node Add Option)
Must be between 0 and 10 (Bottom margin and top margin)
Must be between 0 and 40 (Left margin)
Must be between 21 and 999 (Page length)
Must be between 41 and 240 (Right margin)
Must be greater than -100 and less than +100 (Risk coefficient)
Must be \nnn...\nnn with each nnn between 000 and 255 (Setup
string)
No print-files found in current directory (*.PRN)
No tree data files found in current directory (*.TRE)
Not a TreePlan tree data file: Although the file you selected has
the .TRE extension, its internal format indicates that it was
not created by TreePlan. (File Retrieve Option)
Not enough disk space: The disk you are trying to write to is
nearly full. Press the Escape key repeatedly to return to
READY mode; change the disk or erase unneeded files; retry
the option.
Not enough memory: Although your computer has enough memory to
start TreePlan, you need more memory to use some of
TreePlan's options.
Printer error: The printer is unable to print your table or tree
diagram. Make sure the printer is turned on, securely
connected to your computer, and online.
Printer out of paper
Risk attitude too extreme: The absolute value of the product of
the risk coefficient R times a value or certainty equivalent
cannot exceed 88. Use the Solve Risk Options to change R.
Select node with only one successor branch (Node Shorten Option)
TreePlan User's Manual Page 94
Sum of likelihoods must equal 1.00000: Specify inputs for
Bayesian revision so that the sum of probabilities on each
set of info-event branches equals 1.00000.
Sum of priors must equal 1.00000 (Bayes Input Options)
Sum of probabilities must equal 1.00000
Tree holds only 500 branches: The option you selected would
require a tree with more than 500 branches.
Appendix B: TreePlan Error Messages Page 95
Index
******************************************************************
Action, 8 Name field, 50
Alternative, 8 Nature's tree, 37
Attitude to risk, 21 Node menu options, 61
Backward induction, 16 Partial cash flow, 9
Bayes menu options, 75 Payoff distribution, 12
Bayesian revision, 34 Perfect prediction, 30
Bayes' rule, 37 Posterior probability, 35
Building a tree, 55 Preposterior probability, 36
Print menu options, 70
Certainty equivalent, 12 Prior probability, 35
Chance node, 8 Probability field, 50
Conditional probability, 35 Probability revision, 34
Configuration file, 89
R, 23
Decision node, 8 Revised prior probability, 35
Default menu options, 84 Risk attitude, 21
DriveTek problem, 7 Risk averse, 26
Risk coefficient, 23
Endpoint, 9 Risk neutral, 13
ENGS, 44 Risk profile, 12
Error messages, 92 Risk seeking, 26
Escape key, 5 Risk tolerance, 27
Event node, 8 Rollback method, 16
Event set, 8
EVPI, 30 Sample, 44
EVPI menu options, 73 Sensitivity analysis, 18, 27
EVSI, 44 Simple probability, 35
Expected utility, 22 Solve menu options, 65
Expected value, 13 Standard deviation, 69
Exponential utility, 23 State of information, 36
Extreme R, 66 Strategy, 11
File menu options, 71 Table menu options, 78
Terminal node, 9
Imperfect prediction, 44 Terminal value, 9
Info event, 35
Utility curve, 21
Joint probability, 36 Utility function, 21
Likelihood probability, 35 Valley problem, 30, 38
Lottery, 22 Value field, 50
Main event, 35 Zoom menu options, 89
Marginal probability, 35
Minimum selling price, 12
Modes, 51
TreePlan User's Manual Page 96