I am currently evaluating a mixed research design, where a treatment and a control group are evaluated over time. I am interested in the effectiveness of the treatment and therefore evaluate the significance and size of the interaction effect.
Theoretically it would be important, if the two groups are in fact equal before the treatment. This is not tested in the Mixed-ANOVA, since the maineffect group is pooled over both timepoints.
Is an additional t-test the right way to evaluate this initial equalness of the groups? And would I have to think about some alpha-corrections due to multiple testing?