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two by two
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2022-08-26
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TWO BY TWO CONTINGENCY TABLES
Frequency data are often categorized
by two criteria. For example, a
persons' sex and his political prefer-
ence, or the type of medical treatment
lung cancer patients receive (new or
old) and whether or not one survives
(alive or died).
In the case where each criterion has
exactly two possibilities, a
convenient way to represent the data
is in a 2X2 table.
Suppose that 42 people are called at
random to determine whether there is
any relationship between a person's
sex and whether he will vote
Democratic or Republican in the next
election.
Calls are made at random and the
results tallied as follows:
Of the 25 men contacted, 15 will
vote Democratic and 10 will vote
Republican. Of the 17 women
contacted, 7 will vote Democratic and
10 will vote Republican. These data
can be viewed in the 2X2 table below.
PARTY
Dem Rep
------------------
! ! !
male ! 15 ! 10 ! 25
SEX ------------------
! ! !
female ! 7 ! 10 ! 17
------------------
! ! !
! 22 ! 20 ! 42
! ! !
The question of whether there is a
difference between the voting
preferences of males and females based
on the findings represented by the re-
sults from a small sample is handled
in a field of mathematics called
inferential statistics.
The program included with this
article will calculate several useful
statistics from a 2X2 table.
I assume that the reader understands
the concept of statistical
significance and knows how to test an
hypothesis.
If you don't know how, but you would
like to find out, here are some books:
Statistical Theory and Methodology In
Science and Engineering by Brownlee.
Published by John Wiley and Sons, New
York.
Bancroft's Introduction to Biosta-
tistics by Ipsen and Feigl. Published
by Harper & Row, New York.
Go to your library and find any book
on statistics. Look up CHI-SQUARE.
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