I am running a gyrification analysis between 3 groups.

So I modeled my GLM like the one on this page: https://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf3G0V

I was wondering if it is correct to run a Monte-Carlo correction on the results of the Main effect of group (contrast 4 on the page), which represents an F test if I am correct.

I use the line mri_glmfit-sim --glmdir Results.rh.00.Groupeffectseul --cache 2 abs --cwp 0.05 --2spaces

I get no sig Monte-Carlo corrected results on the main effect of group whereas I find interesting sig results in the one-by-one contrast, which is a bit surprising.

Thank you for your answer.