> According to the 3dMSS, I would create a pred.txt that include label, Time and Group (binarized).
> Are Age and Gender okay to only be in the dataTable (not the pred.txt), and would Gender have to binarized for 3dMSS?
All predictors are required to be specified for prediction (in the file pred.txt). Dummy coding is needed when you want to account for the interaction with nonlinearity (e.g., Group in your case). However, Gender does not have to be dummy-coded.
> I am assuming it has removed the effect from the Group*Time effect.
It does make sense, but it is a little too strong to describe the modeling approach as "correcting" or "removing". I would say "adjusting" or "controlling".
Gang
