Dear all
I suspect this will be a stupid question....but I cannot definitely answer it.....
I have two groups (controls and ALS patients). I'm correlating their FA with their age. I expect a general negative correlation. which should be stronger in the ALS patients (as the disease should increase the FA reduction). so I created this model:
4 regressors (age demeaned across all subjects)
control ALS controls-AGE ALS age
1 0 10 0
1 0 -3 0
.... .... .... .....
.... .... .... .....
.... .... .... .....
0 1 0 3
0 1 0 -1
.... .... .... .....
.... .... .... .....
and set these contrasts
c1 0 0 1 -1
c2 0 0 -1 1
I get the second as significant in many voxels....but the second should tell me that the FA-AGE correlation slope in ALS is higher than in Controls...is it correct ??..it say that is more positive, while I expected instead that it was more negative..that's why I want to be sure about my interpretation....
thanks in advance
Alberto
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