Hello.
I would like some advice regarding a design matrix please.
I have some longitudinal, repeated-measures data which I am running VBM on. In my study, I had three populations, and collected two behavioural measures from each of these. I am using the difference between acquisition, within participant, as the input for Randomise to avoid the issue of exchangeability with repeated measures.
I am interested in looking at the relationship between Group and the behavioural measures. Amongst some of the analyses, one question of interest is to look at whether we can identify the basis of a (behavioural) correlation that exists between the two behavioural measures and, further, if this differs across the groups.
I can see how to compute the simple contrasts for the mean effects, e.g if i had 6 subjects, 2 in each group (note, these are just made up values)
design matrix:
Group1 Group2 Group3 Cov1 Cov2
1 0 0 10 12
1 0 0 12 10
0 1 0 20 15
0 1 0 18 12
0 0 1 9 10
0 0 1 10 12
contrasts:
group1 1 0 0 0 0
group2 0 1 0 0 0
group3 0 0 1 0 0
cov1 0 0 0 1 0
cov2 0 0 0 0 1
(plus reverse contrasts)
The difficulty I'm having is how to identify which brain regions, if any, are correlated across the two measures and whether these differ according to groups.
I'd be grateful of any advice.
Thank you.
Charlotte
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