Dear FSLers,
I would like to perform a Between-Group Analysis of longitudinal VBM data
with 3 groups x 2 repeated measurements (1 baseline & 1 follow-up scan). I
am not quite sure how to build the design matrix:
Say, we have 2 subjects in each group, my design would look like:
*********
/NumWaves 12
/NumPoints 12
/Skip 0
/PPheights 1 1
/Matrix
1 0 0 0 0 0 1 0 0 0 0 0
1 0 0 0 0 0 0 1 0 0 0 0
0 1 0 0 0 0 1 0 0 0 0 0
0 1 0 0 0 0 0 1 0 0 0 0
0 0 1 0 0 0 0 0 1 0 0 0
0 0 1 0 0 0 0 0 0 1 0 0
0 0 0 1 0 0 0 0 1 0 0 0
0 0 0 1 0 0 0 0 0 1 0 0
0 0 0 0 1 0 0 0 0 0 1 0
0 0 0 0 1 0 0 0 0 0 0 1
0 0 0 0 0 1 0 0 0 0 1 0
0 0 0 0 0 1 0 0 0 0 0 1
The first 6 columns model the subject-related variance (rows: 1,3,5,7,9,11
=> baseline; 2,4,6,8,10,12 => follow-up)
the second 6 columns model the interactions between group and
baseline/follow-up.
My contrasts would be:
/NumWaves 12
/NumContrasts 4
/PPheights 1 1
0 0 0 0 0 0 1 -1 0 0 0 0 => Reductions in Group 1
0 0 0 0 0 0 0 0 1 -1 0 0 => Reductions in Group 2
0 0 0 0 0 0 0 0 0 0 1 -1 => Reductions in Group 3
0 0 0 0 0 0 1 -1 -1 1 0 0 => Interaction: "Stronger" reductions in Group 1
versus Group 2
My group description file would be:
/NumWaves 1
/NumPoints 12
/PPheights 1 1
/Matrix
1
1
2
2
3
3
4
4
5
5
6
6
************
Is this correct? Any help would be greatly appreciated!
Best Regards,
Nikos
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