Dear Expert:
If I have a single group of 30 patients with symptom A and symptom B, in these patients TBSS has identified dissociated FA correlation maps with symptom A count and symptom B count separately, and now I just need to be able to directly test the difference of the correlations (the slope) between FA and Symptom A count versus between FA and Symptom B count for these 30 subjects. How should I set up the GLM design matrix?
I know if I treat the Symptom A and Symptom B count scores as independent measures, I can set it up like below (take 10 subjects for example):
EV1 EV2 EV3 EV4
SymA SymB CountA CountB
1 0 2 0
1 0 0 0
1 0 6 0
1 0 1 0
1 0 5 0
0 1 0 1
0 1 0 2
0 1 0 0
0 1 0 7
0 1 0 4
How can I make SymptomA and SymptomB into repeated measures? e.g., Should I make them in one EV and assign 1 and -1 for different symptoms? And for CountA and CountB scores should I keep them as 2 EVs or put them in 1 EV? And I also need to control for each subject's repeated measures effect by adding 30 EVs with value 1 assigned to the 2 symptom scores for each r, right? And what should I put for contrasts if I just need to see the effect of slopeA>slopeB and slopeB>slopeA? My last question is that some of the symptom count is 0 and I assume this wouldn't mess up the design matrix right?
Your help is greatly appreciated,
Yuwen Hung, PhD
McGovern Institute for Brain Research, MIT
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