Less on Third Tee

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• Less on Third Tee
• Moron Con, Tin Gents
• See Tables

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• Lesson 30
• More on Contingency
• Tables

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A 2?2 table can also be used to do a
two-sided test of two proportions
RR 6
Z0 3.2616
4
10.638
As before, reject H0
5
Fishers Exact Test
Used in a 2?2 table when at least one of
the expected frequencies is less than 5
Based on the Hypergeometric distribution

• used to count the number of successes in n
• trials, when the trials are not independent

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Observed
Expected
14.04
24.96
3.96
7.04
?
E1
14.04
?
4.675
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r?c Tables
In general, one variable in a contingency table
can have r levels, and the other can have c levels
The null hypothesis is still that there is
no association or relationship between the
variables
The observed frequencies can be denoted by
Oi
i 1, 2, 3, , rc
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The expected frequencies are calculated as before
The test statistic is
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Spontaneous Abortion
Alcohol Use
E1
7168.67
10
Compare 1-2 drinks to none
Compare 3-6 drinks to none
Compare 7-20 drinks to none
Compare 21 drinks to none