What is a Kruskal Wallis-Test?

Decision-Based Learning - What is a Kruskal Wallis-Test?

1. Kruskal -Wallis Test

2. The non-parametric analogue for a one-way ANOVA test is the Kruskal -Wallis test.

3. The non-parametric analogue for a one-way ANOVA test is the Kruskal -Wallis test. Remember that a non-parametric test is used when the distribution is either highly skewed or we are comparing ordinal or rank ordered data.

4. Example of a skewed distribution 1 2 3 4 5 6

5. Example of rank ordered data Football Players Basketball Players 1 st   2 nd   3 rd 4 th   5 th     6 th   7 th 8 th     9 th   10 th Rank ordered-comparison of amount of pizza slices eaten in one sitting

6. Similar to the Mann-Whitney U test, the Kruskal -Wallis test evaluates the differences among groups by estimating differences in ranks among them.

7. Similar to the Mann-Whitney U test, the Kruskal -Wallis test evaluates the differences among groups by estimating differences in ranks among them . For example, four groups of students, freshman, sophomores, juniors, and seniors might be tested for their preference to watch rugby.

8. The measurement of their preference might be conducted on an ordinal scale with five points on the scale; strong dislike, dislike, neutral, like, and strong like. Such a Like-it scale renders ordinal preference and should be treated with a non-parametric test.

9. The measurement of their preference might be conducted on an ordinal scale with five points on the scale; strong dislike, dislike, neutral, like, and strong like. Such a Like-it scale renders ordinal preference and should be treated with a non-parametric test. Freshmen Sophomores Juniors Seniors strong dislike dislike like strong like dislike Neutral Neutral like strong dislike like like strong like Neutral like strong like Neutral strong dislike Neutral dislike like strong dislike strong dislike like strong like

10. Here is the data rank ordered using the “like it” scale Freshmen Sophomores Juniors Seniors 5 th 4 th 2 nd 1st 4 th 3 rd 3 rd 2 nd 5 th 2 nd 2 nd 1st 3 rd 2 nd 1st 3 rd 5 th 3 rd 4 th 2 nd 5 th 5 th 2 nd 1st

11. As with ANOVA, here we are determining how more than two levels (Freshmen, Sophomores, Juniors, and Seniors) of the independent variable (year in school) compare in terms of the dependent variable (their preference for rugby). preference for Freshman Sophomore Junior Senior

12. Similar to one-way ANOVA, a significant Kruskal -Wallis result should be followed up with post-hoc tests (also non-parametric) to determine where the differences between groups are occurring. preference for Freshman Sophomore Junior Senior