Thanks Stephen,
For each covariate in spm8, I selected:
Interactions: "with Factor 1"
Centering: "Overall mean"
spm8 gives other options for centering:
Factor 1 mean
Factor 2 mean
Factor 3 mean
No centering
User specified value
As implied by Ancova
GM
My understanding was that it is centering on the condition mean so I think this was the correct selection?
Best,
Ryan Herringa, MD, PhD
University of Pittsburgh
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