Dear FSL experts,
I am running TBSS on 2 groups of subjects. The mean ages are not different between the groups. However, when any diffusion metric is plotted over age, the groups show different slopes: one increases with age whereas the other decreases with age. (It looks like an X)
I have combed through the archives and cannot find information about this kind of situation.
1) Should age be used as a covariate in this situation?
2) What does it mean for age to be demeaned within each group versus demeaning both groups using the grand mean? Which should I use in this situation?
Thank you in advance for your time and help!
Cheers,
--Heather
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