Frison and Pocock Stat Med 1992 is the seminal paper. Repeat baseline if and when baseline measures vary, so that taking an average of several measures reduces variance. There are only rare cases where you don’t include the main effect. For instance, if you are comparing weight loss over time in two groups, a main effect would suggest that, 10 seconds after randomization, patients receiving diet 1 are 10 lbs lighter than those on diet 2.
2 Likes