Mann-Whitney Test

A very simple design in quantitative research involves the random allocation of a sample of N individuals to two different groups. The groups are exposed to different treatments, and the research question examines whether there is any difference between the two groups on some criterion variable. Classically, this question is addressed using Student’s t test for independent groups (or the equivalent one-way between-subjects analysis of variance). However, this procedure assumes that the criterion variable in question (a) is measured on an interval or ratio scale, (b) is normally distributed, and (c) has the same variance in both of the groups. The Mann-Whitney test (also known as the Mann-Whitney U test, the Wilcoxon-Mann-Whitney test, the Mann-Whitney-Wilcoxon test, or even simply the Wilcoxon test) was devised for ...