[Freesurfer] Cohen's D = gamma.mgh / rstd.mgh?

Hi there,

What is the correct way to plot, at each vertex, the Cohen's *D* after a *mri_glmfit* comparison? I've seen a few variations posted on the mailing list.

Is gamma.mgh / rstd.mgh is the correct formula? Does rstd.mgh represent pooled SD across both groups (patients and controls)?

Secondly, after plotting the effect size across the whole brain, is it feasible to test whether there are regional differences in effect size by using *mri_segstats* and *aparc* to extract the ROI-averaged effect size in *fsaverage* space, and then perform a paired t-test between say, frontal vs occipital ROIs?

Thank you.

Best Wishes, Elijah