Kruskal–Wallis H-Test for Oneway Analysis of Variance (ANOVA) by Ranks

The Kruskal–Wallis H-Test for Oneway Analysis of Variance (ANOVA) by Ranks is often viewed as the nonparametric equivalent of the parametric Oneway Analysis of Variance (ANOVA). Both the Kruskal–Wallis Test (often using ordinal data) and Oneway ANOVA (typically using interval data) are used to determine if there are statistically significant differences for comparisons of three or more groups. However, avoid seeing these tests as being mere complements of each other. The Kruskal–Wallis Test, as a nonparametric test, is used with ranked data, particularly for when: (1) the data are ordinal and do not meet the precision of interval data, (2) there are serious concerns about extreme deviation from normal distribution, and (3) there is considerable difference in the number of subjects for each comparative group. This lesson addresses the many quality assurance measures that should be attempted before actual implementation of this type of multiple-group comparative inferential analysis.