Non-parametric Kruskal-Wallis test for k independent samples (One-way ANOVA)

Wiki - 2016-05-14

Table of contents

1. What is it ?

2. How to use it on EasyMedStat ?

The Kruskal-Wallis test is a replacement for the Mann-Whitney test when comparing more than 2 independent groups of patients

What is it ?

The Kruskal-Wallis H test (named after William Kruskal and W. Allen Wallis), or One-way ANOVA on ranks is a non-parametric method for testing distributions between independent groups of patients. The H0 hypothesis is that all groups have the same median value, or come from the same population. When rejecting H0, we can say that at least one sample is different from the others, but without saying which one is statistically different.
Since it is a non-parametric method, the Kruskal-Wallis test does not assume a normal distribution of the residuals, unlike the analogous one-way ANOVA, and can then be used with small samples.

How to use it on EasyMedStat ?

On EasyMedStat, you can use the Kruskal-Wallis test with the function Test 2 Variables.

  1. You select a Numeric variable you would like to compare between groups, let's say a functional score (Min = 0, Max = 100), and then you select a List variable to create groups of patients, for example "Dominant hand".

  2. You will get 3 groups of patients : "Right-handed", "Left-handed", "Ambidextrous", with a mean "Total Score" for each group.

  3. A BoxPlot will be displayed and then the Kruskal-Wallis test will be performed, telling you if at least one distribution is different from the others.

NB : If there are only 2 groups to compare (Yes-no variables), another test will be done according to pairing and sample size

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