It is often difficult, particularly when conducting research in psychology, to have
access to large normally distributed samples. Fortunately, there are statistical tests to
compare two independent groups that do not require large normally distributed
samples. The Mann‐Whitney U is one of these tests. In the following work, a summary
of this test is presented. The explanation of the logic underlying this test and its
application are presented. Moreover, the forces and weaknesses of the Mann‐Whitney
U are mentioned. One major limit of the Mann‐Whitney U is that the type I error or
alpha (α) is amplified in a situation of heteroscedasticity.