How To Calculate Critical Value For Mann Whitney U Test

The Mann-Whitney U test, also known as the Wilcoxon rank-sum test, is a non-parametric test used to compare two independent samples. It’s particularly useful when the data is not normally distributed. Calculating the critical value is crucial for determining the statistical significance of your results.

1. Enter the sample sizes (n1 and n2) for the two groups.
2. Select the desired significance level (α).
3. Click the ‘Calculate’ button.
4. View the critical value and chart in the results section.

The Mann-Whitney U test uses the following formula to calculate the test statistic (U):

U = n1 * n2 + (n1 * (n1 + 1)) / 2 - R1

Where:

• n1 and n2 are the sample sizes.
• R1 is the sum of ranks for the first group.

Critical Values for Mann-Whitney U Test (α = 0.05)

n1 + n2	U

• Always check the assumptions of the Mann-Whitney U test before using it.
• Consider using the Wilcoxon signed-rank test for paired samples.

What are the assumptions of the Mann-Whitney U test?

The assumptions are: independence of observations, random sampling, and similar shapes of the population distributions.

Learn more about the Mann-Whitney U test

Understand the Mann-Whitney U test from NIST