[Freesurfer] Some basic cortical thickness questions

Dear All,

I have some basic questions about groups analysis for cortical thickness, and I looked over the list and tutorial, but still have questions. I have two groups, experimental and control, and both were tested before and after training... I plan to use qdec to run the group analysis, and I finished the recon-all, and -qcache processing for each subject. My question is that:

1.Is it necessary to select a ROI prior to my cortical thickness analysis?

2.For the .dat text file, which stats (for cortical thickness) output should I use for the continuous factors such as left hemi thickness, right hemi thickness?

Thanks, Catherine