Mann–Whitney U Test

A good example of a non-parametric test is the Mann-Whitney U-test (Also known as the Mann-Whitney-Wilcoxon (MWW) or Wilcoxon Rank-Sum Test). Unlike its parametric counterpart, the t-test for two samples, this test does not assume that the difference between the samples is normally distributed, or that the variances of the two populations are equal. Thus when the validity of the assumptions of the t-test are not certain, the Mann-Whitney UTest can be used instead and therefore has wider applicability.