Dear freesurfers
my study aims to measure volumetric differences between patients X and controls. As dependent variables, I have (i) a-priori ROIs and (ii) global brain measures (total gm, total wm and CFS). In the ROIs analysis, I use eTVI to control for for head size variability. Now my question is: should I control for head size when measuring overall brain atrophy? Theoretically speaking I'm not sure . Practically speaking there is a high positive correlation (as expected) between global brain measures and eTVI in my sample so I think it wouldn't be correct to use eTVI. But still, is global atrophy affected by head size? should I control for it?
Second quick question: I'm planning to replicate the analysis measuring thickness differences. Should I control for tot mean thickness then?
Thanks in advance for your help.
Gloria