Dear All,
I'm analysing some PET data, and am interested in looking at regions where
activity correlates with RT, and was wondering what was the best way to
proceed.
We have 6 subjects, 12 scans per subject
When I choose the multi-subject covariates only design, there appear to be
two ways to proceed. One is to not have covariate * subject interactions,
to mean centre the RTs, and then to make the following contrasts: 1 to look
at regions where activity correlates with increasing RT and -1 the converse.
The second is to select covariate by subject interactions, and then to have
the following contrasts: 1 1 1 1 1 1 and -1 -1 -1 -1 -1 -1.
Could someone help explain what the differences are between these two
analyses?
Many thanks in advance,
Andrew Lawrence
_______________________________________
Andrew Lawrence PhD,
MRC Cognition and Brain Sciences Unit,
15 Chaucer Rd,
Cambridge CB2 2EF,
UK
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