On 2/19/2022 6:10 PM, fernanda rohrsetzer wrote:

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Hi guys, I'm a beginner in Freesurfer and I want to perform an analysis of the difference between 3 groups in cortical thickness,volume and area having age, mean thickness and etiv as covariate. my design matrix for 3 groups comparison as "1 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 (LR-HR) 1 0 -1 0 0 0 0 0 0 0 0 0 0 0 0 (LR-MDD) 0 1 -1 0 0 0 0 0 0 0 0 0 0 0 0 (HR-MDD)

If possible, I would like to know how my contrasts change when I wish to test the change in thickness with age, after removing the group effects.

It is just move the non-zero values in the contrast to the age columns, like 0 0 0    1 -1 0    0 0 0 0 0 0 0 0 0

Another question I have is how can I create contrasts to control etiv between groups, like 2x2 comparison.

I don't understand. btw, you should normalize your covariates (ie, remove the mean, divide by the sqrt(sum(squares)))

I'm sorry if I was not clear... thanks Fernanda

my FSGD file is GroupDescriptorFile 1 Title MyStudy Class LR Class HR Class MDD Variables age meanThick totalarea eTIV Input Sub001 LR 14.3 1350519.71 1954527.71 1552459.71 Input Sub002 MDD 15.7 1558515.86 1689767.98 1809809.87

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