[Freesurfer] Group Analysis Age slopes

Hi Doug,

I ran a group analysis comparing a trait between two groups (Diseased vs Controls) with one continuous variable (age), with the following design matrices [1 -1 0 0] and [0 0 1 -1]. When I loaded the significance map and the descriptor file, the age slope of the trait in Controls was positive whereas the age slope of the trait in the Diseased cases was negative. Therefore, comparing the intercept between the two groups does not really give that much info, since the slopes are of opposite sign. What do you believe would be the best course of action in order to compare the age-corrected traits: 1) instead of age=0 maybe comparing the groups at age=mean? 2) or going with a DOSS model?

Thank you for your time, Panos