Sphericity violation in RM anova
When we perform the Greenhouse adjustment, is it automatically applied to subsequent posthocs? Or should any additional steps be done?
How should posthoc results be reported in an article after a Greenhouse correction?
Comments
Hi.
It is not possible to calculate sphericity separately for each of the levels of your four-level repeated-measures ANOVA. Sphericity is a characteristic of the entire model, not of any particular level of the repeated-measures factor.
Also, Welch's ANOVA is for between-subjects factors only. it cannot be applied to a repeated-measures factor.
Regarding assumption-violation more generally, I would see the following:
https://forum.cogsci.nl/discussion/8822/kolmogorov-and-levene
https://forum.jamovi.org/viewtopic.php?t=2731
R
If you run a repeated-measures ANOVA with and without corrections for sphericity violation, you'll see that the corrections do not impact the post-hoc tests. There's nothing more to be done, since the question of sphericity doesn't apply to a repeated-measures comparison in which there are only two levels (which is the case when does a post-hoc comparison).
R
@johndavid2 What is a large language model? :-)
R