I am trying to perform a paired analysis for a data set that has subjects' who belong to either group1 or group2 and have data at time point1 (tp1) and time point2 (tp2). I am following all the steps on the wiki but I want to clarify if the contrasts I plan to use for my analyses are appropriate.

For my analyses, I only have two groups and no covariates. I am interested to know if the decrease in cortical thickness of subjects in group 1 across tp1 and tp2 is more than the decrease in cortical thickness of subjects in group 2 across tp1 and tp2. The contrast I think should be used for this is: 1 -1. Is that correct?

I am also interested to know if the cortical thickness decreased for subjects regardless of the groups so should I use the contrast: 1 for that?