Thank you for your suggestions Bruce and Mike.
Mike, could you please provide the motivation behind your suggestion of using mean cortical thickness as a covariate ?
Let's consider this is the context of a simple example. Let's say we compare the mean thickness of the pre-central gyrus in patients versus controls. Does the biology suggest that even after one accounts for age and gender, there are natural variations in the gyrus thickness measurements ( that is, some people would just happen to have larger thickness measurements ) ?
If this is the case, then one could normalize the thickness of the individual gyrus measurement (pre-central gyrus in this example) with the mean cortical thickness. However, in most of the papers I have only seen age and gender used as co-variates.
Thanks Mehul
On Sun, Nov 1, 2009 at 4:44 PM, Michael Harms mharms@conte.wustl.eduwrote:
To me, it makes much more sense to use mean cortical thickness as a covariate for thickness-based analyses.
cheers, Mike H.
Hi Mehul,
the MNI group had an abstract showing that thickness didn't need eTIV correction at HBM a number of years ago, and it has been our experience as well.
cheers, Bruce
On Sat, 31 Oct 2009, Mehul Sampat wrote:
Hi Folks,
If am comparing the mean thickness for certain gyri (pre-central, post-central) in a controls versus patients. I obtain the thickness measurements from lh.aparc.a2009s.stats and rh.aparc.a2009s.stats I was wondering if I need to normalize these thickness measurement with the estimated total intracranial volume (eTIV) ?
Or has anyone reported that the these are independent of eTIV ? If so then as I understand I would only need to account for age and gender in any subsequent analysis using GLM.
Thanks Mehul
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