I have 4 separated groups (4 different interventions), and I measured the dependent variable over 4 time points. I considered my intervention groups as "between subjects factor" and the time points as "within subjects factor". I realized that there was a significant difference in pre-test.
So I chose this method: mixed ANCOVA with repaeted measures: 4 (intervention groups, between subject factor) * 3 (time points, within subject factor), and the pre-test as covariate (in order to control initial differences)
My consulting adviser said it is false, because there are more than 2 time points and we can't use ANCOVA in this case.
Is it wrong or right? If it's wrong, would you suggest me any appropriate method, please?