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.edu> wrote:

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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