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This is a nonparametric test of the hypothesis that the two subpopulations, machine and hand counts, come from the same distribution.

        Wilcoxon rank sum test

data:  (Clinton..d - Obama..d)[machines] and (Clinton..d - Obama..d)[!machines]
W = 422, p-value = 0.0001150
alternative hypothesis: true mu is not equal to 0
95 percent confidence interval:
 0.1186801 0.2903706
sample estimates:
difference in location

The test is astonishingly simple: you rank the combined population and add up the ranks of the elements of one of the two subpopulations, and then look up in a table. This is telling us that the Hillsborough hand counts and the machine counts come from different populations at 99.99% confidence level.

We have met the enemy, and he is us — Pogo
by Carrie (migeru at eurotrib dot com) on Thu Jan 17th, 2008 at 11:42:29 AM EST
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