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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Hi,
When conducting group-level analysis, for example comparing volumetric differences or tractography FA across subjects between groups. How we correct for the size of the brain when comparing volumetric differences or correct for the whole brain FA? Thank you so much!
Best, Qi