Dear SPM experts,
I already run a flexible factorial design with 2 groups (n1=17, n2=12) and 2 within-subject conditions. This is a VBM longitudinal analysis and here are the factors:
Factor 1: Subject
Factor 2: Group (2 Levels)
Factor 3: Time (2 Levels)
Covariate1: age
Covariate2: total intracranial volume
I set up the following contrasts:
F tests:
Time differences in Group1: 1 -1 0 0
Time differences in Group2: 0 0 1 -1
Main Effect Time: 1 -1 1 -1
Main Effect Group: ones(1,2)/2 -ones(1,2)/2 0 0 ones(1,17)/17-ones(1,12)/12
Interaction Time by Group: 1 -1 -1 1
I think all of these should be correct but when I entered the contrasts weights for Main Effect of Group, I got the "Invalid contrast" error.
Could anyone explain me why this is happening and what would be the correct contrast weights matrix for this, please?
Thank you in advance for your help.
Best,
Noelia
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