External Email - Use Caution
<This is an updated repost>
Dear Freesurfers,
I have a simple design with patients and controls and would like to
find regions showing group differences in cortical volume and
thickness. I also remove the effect of age, sex and ICV. Running the
GLM group analysis by the book I get a few clusters showing
significant differences in intercept.
1. I interpret this like patients have smaller “predicted” regional
volume at age 0, or at mean age of the group (if demeaned age
covariate) compared to controls. How can this finding be described in
a more clinically meaningful way?
2. Related to the above, how do I visualize what is going on in the
significant clusters? The extracted values from these clusters
(ocn.dat) show no group differences in volume when displaying the
group means in SPSS (using either age/sex/ICV adjusted or non-adjusted
values). Maybe I am misunderstanding something, how can there be
differences in intercept but no differences between group means?
(slopes not significantly different). How do I best describe and
visualize this group difference in a paper?
Going through the studies I found on Pubmed that used Freesurfer with
vertex-wise GLM, so far, I only found e.g. the “lower thickness”
interpretation in one group vs the other and not “lower intercept”. In
my case at least I cannot say this since the extracted values between
groups show no group difference.
Julian