Hi good SPM users,
Newbie to SPM looking for some elementary advice. I want to run an ANCOVA in SPM2 to control for gender across 2 groups. When I try, my design matrix has a constant mean column, which my supervisors tell me should not be there because "if the input (as we have) is a contrast image i.e. a subtraction of conditions, then they already have effectively removed differences in the mean activity per subject at the first level (they are 'difference socres'), so we don't need to add the constant term at the second level".
Can anyone provide input? Thanks for your time.
Garret (Edinburgh)
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