Hi Anderson,
Thank you for clearing that up.
I have a few more follow-up clarification questions.
1) If I were to subtract the first time point from the second time point (and we're talking about DTI scalar images projected to tract skeletons), would I subtract the DTI scalar images before they're projected to the tract skeleton or the DTI scalar values that have been projected to the skeleton?
2) If I understand you correctly, evaluating the change between time points would be an unpaired t-test once again where the design matrix would have the same number of rows as subjects. If I wanted to use include nuisance covariates (age, sex, etc) would I use the value from the first time point? I guess this question mainly concerns age...
3) If I evaluate change between time points, does this allow me to include subjects who were scanned at irregular intervals because I can now annualise the change (divide by number of years)? With the design matrix in my previous message, I was originally only going to use subjects scanned at a 2 year interval and not use those scanned at a 1 year interval.
Thank you,
Joy
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