Dear SPM experts,
I would like to compare the fMRI activity during a task in three groups and check if the differences between groups A and B are bigger/smaller than the differences between groups A and C. I did an F test with the following weights matrix:
[2 – 1 -1
-1 2 -1
-1 -1 2]
and this one:
[1 -1 0
0 1 -1]
and then I did t-tests to compare the groups between them so: [0 -1 1]; [1 0 -1] etc. But that doesn’t really answer my question since it only represents the differences between two groups independently. Would you know which contrasts to use to check if the differences in activations between two groups (A and B) are bigger/smaller than between two other groups (A and C)? Maybe I can see that by plotting?
Thanks a lot in advance,
Ariadna
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