QQ-Plot Repeated Measures ANOVA

Discuss statistics related things

by Lea » Tue May 11, 2021 7:29 am

Hi Jamovi Team,
my student uses Jamovi for her thesis and she reported a strange QQ-Plot for a repeated measures ANOVA: Image. (https://ibb.co/tDxpx4H)
It seems to me that somehow the dots are the unstandardized residuals, but the line is based on the standardized ones. If I just looked at the QQ-Plots from the two separate variables (via Descriptives), the lines actually go through the dots, so the variables look fine to me.

I checked the QQ-Plots in R (fitting a mixed model), using performance::model_check(). Here the line actually matches the dots:
Image (https://ibb.co/bRP2KL7)

Finally, I made a QQ-Plot with the unstandardized residuals and the lines for both the standardized and unstandardized residuals, and you can see that the combination of unstandardized dots and standardized line matches Jamovi's QQ-Plot:
Image (https://ibb.co/wJPw6Vc)

So could it be that there is an error in the QQ-Plot code? Or am I missing something?

(The first QQ-Plot is from a "reduced" rm Anova with only one 2-level factor as predictor to replicate the problem. These are actually count data, but my student wanted to know whether they are "normal" enough to analyze with an Anova for her thesis. I also don't think that this is relevant for the problem, but who knows.)
Posts: 1
Joined: Mon May 10, 2021 2:13 pm

Return to Statistics