Wilcoxon rank-sum test

n. A nonparametric test of the similarity of two distributions in which the absolute difference between pairs of scores is found and then ranked, and the ranks of the positive and negative differences are summed. If there is no difference between the distributions, the two sums should be nearly equal. The statistic is calculated by the formula

$ \frac{n(n-1)/4-T}{\sqrt{n(n+2)(2n+1)/24}} $

where \(T\) is the smaller of the two summed ranks and \(n\) is the number of pairs in the sample.