Hi Jay -
What exactly are you wanting to test?
You are not actually modelling or testing differences in grey matter between groups. For this need additional regressors modelling the mean of each group (e.g. comprising of 1s and 0s).
Your first four contrasts look for differences across groups in the correlation between your variables and grey matter (e.g. an interaction). You first might want to include a contrast looking for whether there is a correlation at all. The next contrasts are not really meaningful as they are just averaging differences in correlations of the two variables, which may have quite different scales.
Eugene
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Centre for Functional MRI of the Brain (FMRIB) | University of Oxford
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On 9 October 2010 15:26, Jay Ives
<[log in to unmask]> wrote:
Hi,
I apologise for asking advice on this, but I would be grateful for guidance on setting up design files. I have read the available documentation and many postings to the archive, but remain confused. A robust tutorial would be most welcome.
Anyway, I have a VBM study with 2 groups and some scores from tests available as continuous variable. I want to test the variables separately and combined.
I have made a design.mat file with groups 1 and 2, and variable values replacing the x's and y's
1 x 0 y 0
1 x 0 y 0
1 x 0 y 0
2 0 x 0 y
2 0 x 0 y
2 0 x 0 y
and a design.con file
1 -1 0 0
-1 1 0 0
0 0 1 -1
0 0 -1 1
1 -1 1 -1
-1 1 -1 1
Am I on the right track?
Thx....J