Dear all,

I’m relatively new with Freesurfer, but slowly getting more and more used to it’s great possibilities. To be ‘sure’, I’ve a question about the design of a GLM.

I want to compare CT in Healthy Controls vs Diseased, and control for age and sex. It appears to me that factors (eg sex) cannot be used as covariate/variable, which forces me to model them as a separate class although I’m not interested in sex differences. This brings me to the following FSGD file:

# HcDis.fsgd

GroupDescriptorFile 1

Title HcDis

Class Hc_Male

Class Hc_Female

Class Dis_Male

Class Dis_Female

Variables Age

Input subjid1 Hc_Male 35

Input subjid2 Dis_Female 30

….

Then the difference between Hc and Dis, corrected for age and sex is given by the contrast matrix

#Hc-vs-Dis.mtx

0.5 0.5 -0.5 -0.5 0 0 0 0 0 0 0 0

Is this correct?

Best,

Martijn