Afsnitsforfatter: Danielle J. Navarro and David R. Foxcroft

The Friedman non-parametric repeated measures ANOVA test

The Friedman test is a non-parametric version of a repeated measures ANOVA and can be used instead of the Kruskall-Wallis test when testing for differences between three or more groups where the same participants are in each group, or each participant is closely matched with participants in other conditions. If the dependent variable is ordinal , or if the assumption of normality is not met, then the Friedman test can be used.

figur 165 Repeated Measures ANOVA (Non-parametric) dialogue box in jamovi

As with the Kruskall-Wallis test, the underlying mathematics is complicated, and will not be presented here. For the purpose of this book, it is sufficient to note that jamovi calculates the tie-corrected version of the Friedman test, and in figur 165 there is an example using the Broca’s Aphasia data we have already looked at.

It is pretty straightforward to run a Friedman test in jamovi. Just select Analyses → ANOVA → Repeated Measures ANOVA (Non-parametric), as in figur 165. Then highlight and transfer the names of the repeated measures variables you wish to compare (Speech, Conceptual, Syntax) into the Measures: text box. To produce descriptive statistics (means and medians) for the three repeated measures variables, click on the Descriptives button.

The jamovi results show descriptive statistics, χ²-value, degrees of freedom, and the p-value (figur 165). Since the p-value is less than the level conventionally used to determine significance (p < 0.05), we can conclude that Broca’s Aphasics perform reasonably well on speech production (Md [median] = 7.5) and language comprehension (Md = 6.5) tasks. However, their performance was considerably worse on the syntax task (Md = 4.5), with a significant difference in post-hoc tests between Speech and Syntax task performance.