Hi Kelly, See also these threads where I advocate using mean cortical thickness as an appropriate covariate for a thickness analysis:

http://www.mail-archive.com/freesurfer@nmr.mgh.harvard.edu/msg11987.html http://www.mail-archive.com/freesurfer@nmr.mgh.harvard.edu/msg13459.html

Mean cortical thickness is easily obtained using the cortex.label files in conjunction with mris_anatomical_stats

cheers, -MH

On Fri, 2010-05-28 at 08:32 -0400, Bruce Fischl wrote:

Hi Kelly,

it's a bit of an open question what the relationshop between thickness and icv is. It's probably not linear, maybe icv^(1/3)?

cheers Bruce

On Fri, 28 May 2010, Kelly Silva wrote:

...

Hello,

I'm doing regression analyses with cortical thickness at the level of voxel. Should I correct the total GM volume by introducing this parameter as a confounding variable? Shoud I include the intracranial volume as an additional nuisance variable? If positive, I assume that these variables can only be introduced as covariates if they differ between groups. Am I correct?

I saw in one message that we should not corret for thickness. Why not?

                                       Thanks in advance and best regards,
                                                                 Kelly

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