Dear Eelco

years ago i posed a similar question on the FS email list

https://mail.nmr.mgh.harvard.edu/pipermail//freesurfer/2011-November/021386.html

a part of the response is below

>>> The other question is how mri_glmfit estimates the variance. Because I have
>>> only one subject in the patient group, there is not variance in that group
>>> and therefore I guess mri_glmfit used pooled (across both groups) estimates
>>> of variance, isn't it?
>>>   
>>>       
>> Yes, it uses pooled estimates.
>>
>> doug

if you are concerned with respect to the variance estimates, it does not matter because variance is estimated pooledly, i.e. across both groups.

hope this helps

Cheers

Jürgen

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Am 13.10.2016 um 15:56 schrieb Eelco van Duinkerken:

Hi all,

I am using FS with data from 2 different studies that were acquired on the same MRI-machine with the same T1 and FLAIR sequences. Unfortunately, the group sizes are not very balanced, with 31 controls, 16 obese and 32 diabetes patients.

Is the GLM for thickness used in FS very sensitive to this unequal group size?

Thanks for the help,

Eelco

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