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[patch #5583] NPAR TESTS

From: Jason H Stover
Subject: [patch #5583] NPAR TESTS
Date: Fri, 15 Dec 2006 22:12:38 +0000
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20061025 Firefox/

Follow-up Comment #9, patch #5583 (project pspp):

Your p-value of 1.0 below is ifne, though it does point to a 
quirk of p-values. The p-value of 1.0 means this: Under the hypothesis that
the distribution of the sexes is equal, the probability
of seeing a "more extreme" test statistic than 10 males/10 females is 1.0.
Perhaps it should be 

1-Pr(10 males) = 1 - (20 choose 10) * (1/2048)

...but that isn't how p-values are defined. They are defined to
include the observed value of the test statistic in their computation, so we
have a p-value of

Pr ({less than or equal to 10 males} \cup {more than 10 males})

...which is 1.0 for a binomial random variable with 20 trials and
null hypothesis success probability of 0.5.


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