Forfatter av avsnitt: Danielle J. Navarro and David R. Foxcroft

Friedmans ikke-parametriske ANOVA for gjentatte målinger

Friedman-testen er en ikke-parametrisk versjon av en ANOVA for gjentatte målinger og kan brukes i stedet for Kruskall-Wallis-testen når man tester for forskjeller mellom tre eller flere grupper der de samme deltakerne er i hver gruppe, eller der hver deltaker er tett matchet med deltakere i andre betingelser. Hvis den avhengige variabelen er ordinal , eller hvis forutsetningen om normalfordeling ikke er oppfylt, kan Friedman-testen brukes.

Fig. 165 Dialogboksen Repeated Measures ANOVA (Non-parametric) i 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 Fig. 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 Fig. 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 (Fig. 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.