Mann Whitney U test in R is a useful tool for comparing two independent samples when the parametric assumptions of the t-test are not met. For example, we might use it to compare the performance of two groups of participants on a cognitive task that produces ordinal or skewed data. In this post, we will explain how to perform and interpret the Mann Whitney U test in R and show some examples of its application in cognitive psychology. To perform the Mann Whitney U test we can use the `wilcoxon