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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