Overview for Kruskal-Wallis Test

Use Kruskal-Wallis Test to determine whether the medians of two or more groups differ. Your data must have one categorical factor, a continuous response, and the data for all of the groups must have similarly shaped distributions.

For example, a health administrator wants to compare the number of unoccupied beds in three hospitals. The administrator randomly selects 11 days and lists the number of unoccupied beds for each day. To determine whether the median number of unoccupied beds differs, the administrator uses the Kruskal-Wallis test.

Where to find this analysis

To perform the Kruskal-Wallis test, choose Stat > Nonparametrics > Kruskal-Wallis.

When to use an alternate analysis

  • If your data meet the following sample size guidelines, consider using One-Way ANOVA because it will perform very well with skewed and nonnormal distributions, and it has more power.
    • The data contain 2–9 groups and the sample size for each group is at least 15.
    • The data contain 10–12 groups and the sample size for each group is at least 20.
  • If the distributions of the groups include outliers, use Mood’s Median Test.
  • If you have a randomized block design and want to test the medians, use Friedman Test.
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