I am using SPM96 to perform a conditions and covariates analysis in a PET FDG
study. I have two sessions per subject, one scan per session, and a single task
performance measure for each scan. The first session is the control condition,
the second session is the active condition.
I would like to test for correlations between the change covariate scores
across the two scans/sessions with the change in the PET images. I have
followed the recomendation of Andrew Holmes of creating a mean-centered
covariate difference score and entered the covariate as -1*Difference/2 and
+1*Difference/2.
My question is what is the interpretation of using or not using a condition
specific fit, and which approach is more appropriate to my design.
If I use a condition specific fit I set the contrasts for the correlation
analysis as:
0 0 -1 1 and 0 0 1 -1
The contrasts when not using the specific fit are:
0 0 1 and 0 0 -1
Thank you. BTW, it is not feasible for me to use SPM99b at this point.
sg
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