You have 16 groups so you need 16 items in the contrast vector (assuming no continuous variables), so you need something like
-1 +1 repeated 8 times to give you 16

On 11/17/2021 7:23 AM, Thalhammer, Melissa wrote:

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Dear Freesurfers,

I am struggling with the group analysis (FT vs. PT) to investigate cortical thickness while correcting for scanner (4 sites) and sex. I have posted a question already regarding the handling of discrete variables and I got to know that all discrete variables should be treated as classes rather than variables in the FSGD file. However, I have difficulties implementing the correct Contrast file right now. My classes are the following:

PTMaleScanner1

FTMaleScanner1

PTMaleScanner2

FTMaleScanner2

PTMaleScanner3

FTMaleScanner3

PTMaleScanner4

FTMaleScanner4

PTFemaleScanner1

FTFemaleScanner1

PTFemaleScanner2

FTFemaleScanner2

PTFemaleScanner3

FTFemaleScanner3

PTFemaleScanner4

FTFemaleScanner4

where the two groups FT vs. PT should be compared while regressing out scanner and sex. As far as I understood, we need "1 -1" for the group difference as well as "1 -1" for the gender difference. But how should the complete contrast matrix look like? Thank you in advance!

Best,

Melissa
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