Dear Alfonso,

Thanks for your reply. Regarding the interaction, to identify the direction of slope for each variable I have to do further analysis separately for each trait_group, right? For example, I have to use the following model again, however with contrasts [0 0 0 1 0] to identify slope for trait_F and [0 0 0 0 1] for the trait_M.

y ~ group_F + group_M + covar1 + trait_F + trait_M


Bests,
Amir