Statistics-Test-WilcoxonRankSum version 0.0.1 Performs the Wilcoxon (aka Mann-Whitney) rank sum test on two sets of numeric data. In statistics, the Mann-Whitney U test (also called the Mann-Whitney-Wilcoxon (MWW), Wilcoxon rank-sum test, or Wilcoxon-Mann-Whitney test) is a non-parametric test for assessing whether two samples of observations come from the same distribution. The null hypothesis is that the two samples are drawn from a single population, and therefore that their probability distributions are equal. See the Wikipedia entry http://en.wikipedia.org/wiki/Mann-Whitney_U (for eg.) or statistic textbooks for further details. When the sample sizes are small the probability can be computed directly. For larger samples usually a normal approximation is used. Input to the test are two sets (lists) of numbers. The values of both lists are ranked from the smallest to the largest, while remembering which set the items come from. When the values are the same, they get an average rank. For each of the sample sets, we compute the rank sum. Under the assumption that the two samples come from the same population, the rank sum of the first set should be close to the value B, where n1 and n2 are the sample sizes. The test computes the (exact, resp. approximated) probability of the actual rank sum against the expected value (which is the one given above). So, when the computed probability is below 0.05, we can reject the null hypothesis at level 0.05 and conclude that the two samples are significantly different. The implementation follows the mechanics described above. The exact probability is computed for sample sizes less than 20, but this threshold can be set with `new'. For larger samples the probability is computed by normal approximation. INSTALLATION To install this module, run the following commands: perl Makefile.PL make make test make install Alternatively, to install with Module::Build, you can use the following commands: perl Build.PL ./Build ./Build test ./Build install DEPENDENCIES uses the following: Carp Carp::Assert Class::Std Contextual::Return Set::Partition List::Util qw(sum) Math::BigFloat Math::Counting Statistics::Distributions COPYRIGHT AND LICENCE Copyright (C) 2008, Ingrid Falk This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.