Dear Alfonso,

Thank you very much for your kind reply, it's very helpful!

I have a follow-up question. When we compare regression between 2 groups (using one-way ANCOVA covariate interaction: 0 0 1 -1 for group1, group2, covariateForGroup1, covariateForGroup2), what measure of effect size is applicable? Can we use Cohen's f = |T|/sqrt(dof) in this case? 

Grateful for your help,

Yana