Hi Qi - Correcting for overall brain size is important when you are comparing measures of length/area/volume. As in, you want to know if a region specifically is bigger in population A vs. B, and not just because the whole brain is bigger. In that case, use eTIV (estimated total intracranial volume) from the freesurfer segmentation stats.

FA is not measuring size of a region, so correcting for brain size is less of an issue there. It's a possibility perhaps that for someone with a substantially smaller brain there may be more partial voluming affecting FA, so it can't hurt to check for an effect before including it in your analysis.

Anastasia.

From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> on behalf of Zeng, Qi <qi.zeng@icahn.mssm.edu>
Sent: Monday, August 31, 2020 11:44 AM
To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] group level analysis

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