Dear Karl,
>In fact the second-level analysis, used in SPM, assumes that the design
>matrices are identical for each subject.
I've seen this point mentioned before but I think I may have missed its
importance.
Does this mean that if you randomize the order of presentation across
subjects then
you cannot use an RFX because each subject has a different design matrix?
I think
this is rarely done in fMRI studies but it is normal practice for PET. I'm
wondering
whether this means that the assumptions underlying an RFX analysis are
violated
when analysing (typical) PET data.
Would it make a difference if one analysed a group of subjects (with
different stimuli
presentation ordering) using the 'conditions x subj' option before
generating the subject-
specific contrasts? In that case, each subject would be part of the same
design matrix
although the contrasts would come from independent (and different) subsets.
Thanks.
- Joe
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