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Hi Carly,

plus, if I may answer in addition, make sure that the ICV differences are checked with sex as covariate,

so that statement of yours is only valid, if analyzed also per sex separately, or with sex as covariate.

Next, you should also (once) test for ICV-by-Dgx effects, as you cannot know in advance, if the relationship

between ICV and local measures is the same.

Best,

Philipp Sämann

________________________________ Von: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu im Auftrag von Iglesias Gonzalez, Juan E. JIGLESIASGONZALEZ@MGH.HARVARD.EDU Gesendet: Montag, 8. Juli 2024 19:39 An: Freesurfer support list Betreff: Re: [Freesurfer] Is ICV needed as a covariate if matched between groups

It’s always a good idea to divide the volumes by ICV (or add ICV as a regressor). This is very unlikely, but what if your controls happened to have smaller heads than your patients? For peace of mind, I’d correct by ICV.

Cheers,

/Eugenio

--

Juan Eugenio Iglesias

http://www.jeiglesias.com

From: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu on behalf of Carly McIntyre-Wood mcintc10@mcmaster.ca Date: Monday, July 8, 2024 at 12:06 PM To: freesurfer@nmr.mgh.harvard.edu freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] Is ICV needed as a covariate if matched between groups

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Hi there,

I am investigating differences in hipp/amyg volume between a patient and HC sample and am wondering if there is any reason I would still need to include ICV as a covariate if the groups do not differ on ICV (p=.793).

Thanks so much,

Carly