In the context of nonparametric tests, what does the Mann-Whitney U Test assess?

The Mann-Whitney U Test is used to assess whether there is a difference in the distributions of two independent samples, particularly focusing on the medians of those samples. This nonparametric test does not assume a normal distribution of the data, making it suitable for ordinal data or when the sample sizes are small. By ranking all the data points from both samples together and comparing the sum of the ranks for each group, the test effectively evaluates whether one sample tends to have larger values than the other.

While the test is related to the concept of medians due to its ranking method, it is important to note that it provides insights into the entire distribution rather than just comparing means or variances. This characteristic is what differentiates it from parametric tests that specifically target those statistical measures, emphasizing the adaptability of the Mann-Whitney U Test in analyzing data that may not meet parametric test assumptions.