Performing a Mann-Whitney test of two numeric columns’ medians

A Mann-Whitney test indicates whether values tend to be larger in one of two columns. If the values are drawn from distributions having the same shape but different locations, the Mann-Whitney test can be interpreted as a test of whether the column medians are equal.

To perform a Mann-Whitney test:

  1. In the Summary view, use the confidence slider to choose a desired confidence level
  2. Command-click two numeric columns of interest on the left
  3. Click the button labeled Boxes below the Covariate view
  4. The result of the Mann-Whitney test will appear in the Bottom Line

Note that even if the observed medians are equal across categories, the Mann-Whitney test can indicate that the population medians are not equal. This is most likely due to the distribution of values differing across columns.

To analyze differences in three or more numeric columns’ medians, use a Kruskal-Wallis test.

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