[Freesurfer] Qdec Questions

Hi all,

I'm running analyses in Qdec and want to verify a few things:

1. When comparing two groups (HC vs patients) I am including mean cortical thickness as a covariate, using the following equation:

bh.thickness = (lh.thickness*lh.surfarea + rh.thickness*rh.surfarea) / (lh.surfarea + rh.surfarea)

Is this the best way to calculate global mean thickness?

2. I want to regress out any effects of age, therefore I need to demean the ages for my groups as a whole, and not perform this calculation on each group separately, correct?

3. I'm including questionnaires as a covariate of interest - do I need to demean these values as well?

Thank you in advance for your help!

Ashley