The MannWhitney U Test is a nonparametric statistical test used to compare two independent groups when the data is not normally distributed or the variances are unequal. The MannWhitney U Table provides critical values for interpreting the results of this test.
What it contains:
 Sample sizes (n1 and n2): The number of observations in each group.
 Significance level (α): The probability of rejecting the null hypothesis (H0) when it’s actually true, typically set at 0.05 (5%) or 0.01 (1%).
 Critical values for U: These are specific thresholds for your calculated MannWhitney U statistic based on n1, n2, and α. There are separate tables for twotailed and onetailed tests.
How to use it:

Calculate your MannWhitney U statistic: This involves ranking the combined data set and assigning ranks to each observation based on its group membership.

Identify the appropriate section: Twotailed table for comparing differences in any direction, onetailed table if you have a specific direction in mind (e.g., only larger values in one group).

Locate the row with your sample sizes (n1 and n2).

Find the column with your chosen significance level (α).

Compare your calculated U statistic to the critical value:
 Twotailed test: If your U is less than or equal to the critical value, reject the null hypothesis (H0) and conclude that there is a significant difference between the two groups.
 Onetailed test: Double your chosen α and use the table accordingly. Reject H0 if U is less than or equal to (for lower values in one group) or greater than or equal to (for higher values in one group) the adjusted critical value.
Alpha = .01 (twotailed)
Alpha = .05 (twotailed)
Alpha = .10 (twotailed)