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PC-EMS
A Program for Sample Size Determinations
Version 1.0
September 2, 1985
Gerard E. Dallal
USDA Human Nutrition Research Center on Aging
at Tufts University
711 Washington Street
Boston, MA 02111
and
Tufts University School of Nutrition
132 Curtis Street
Medford, MA 02155
PC-EMS uses the algorithm of Cornfield and Tukey(1956) to
calculate tables of Expected Mean Squares for balanced
experiments.
Models are entered as per the following example:
T,G,S(G),TG,TS(G)
or
T + G + S(G) + TG + TS(G)
where
T and G are the main effects of T and G,
S(G) is the effect of S within G,
TG is the interaction between T and G, and
TS(G) is the interaction between T and S(G).
Terms are separated by '+' or ','. Imbedded blanks are
optional. The grand mean and error term are NOT stated
explicitly.
NOTICE
Program and documentation copyright 1985 by Gerard E. Dallal.
Reproduction of material for non-commercial purposes is
permitted, without charge, provided that suitable reference
is made to PC-EMS and its author.
Neither PC-EMS nor its documentation should be modified in
any way without permission from the author, except for those
changes that are essential to move PC-EMS to another
computer.
Please acknowledge PC-EMS in any manuscript that uses its
calculations.
OPERATION
1. Each factor is represented by label consisting of a
single letter. PC-EMS distinguishes between upper and
lower case letters.
2. Interactions are denoted by placing the labels for the
appropriate factors side-by-side, as in AB. Do NOT use
asterisks, as in A*B. The asterisk will be interpreted
as a factor label.
3. Nested effects are indicated using the standard
convention, i.e., S(G) denotes S within G.
LIMITATIONS
1. The model must fit on one line and contain no more than
79 characters including imbedded blanks.
2. A model may contain no more than 10 factors (main
effects) or 50 terms.
3. A single term may contain no more than 10 characters
(including parentheses).
INSTALLATION
PC-SIZE is written for the IBM-PC. Installation on a new
computer may entail modifying the following statements:
The first DATA statement:
IIN -- input unit number (screen)
IOUT -- output unit number (screen)
IWOUT -- save file unit number
The OPEN statement for the save file just before statement
10.
EXAMPLE
Models are entered in the form:
A + B(A) + C + AC + B(A)C
Terms must be separated by '+' or ',' ; blanks are optional.
Grand mean and error term are NOT stated explicitly.
Enter the model:
T,G,S(G),TG,TS(G)
Enter the number of levels of T : 3
Enter the number of levels of G : 2
Enter the number of levels of S : 4
Is the factor T fixed (F) or random (R)? F
Is the factor G fixed (F) or random (R)? F
Is the factor S fixed (F) or random (R)? R
Enter the number of observations per cell: 1
EMS(T) = 1 * error + 1 * TS(G) + 8 * T
EMS(G) = 1 * error + 3 * S(G) + 12 * G
EMS(S(G)) = 1 * error + 3 * S(G)
EMS(TG) = 1 * error + 1 * TS(G) + 4 * TG
EMS(TS(G)) = 1 * error + 1 * TS(G)
EMS(error) = 1 * error
REFERENCES
Cornfield, J., and J.W. Tukey (1956). Average values of mean
squares in factorials. The Annals of Mathematical
Statistics,27,907-949.