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Dear Freesurfer experts,
We are investigating brain structure differences between 2 groups. We are using Gray Matter Volume and Cortical Surface Area as structural measures and want to look at specific ROIs. We want to include Sex, Age and TIV as covariates. However, we are unsure if we should correct for TIV when using Cortical Surface Area or only when using Gray Matter Volume. We would be very happy about any kind of help or literature regarding this question!
Additionally, we have calculated a whole brain GLM analysis and found significant differences between groups. After inclusion of covariates, no result remained significant. However, when using an ROI approach including the same covariates, the results strongly indicated between group differences. Does anyone have an idea on why this could be the case?
Thank you very much for your help!
Best, Magdalena, Helena & Federica