Repeated Measures ANCOVA
I am trying to do an ANCOVA per my advisor's recommendation, but I am not sure how to proceed here:
I have two treatments (A and B). All participants completed both treatments on separate days (within-subjects design). Participants completed the same cognitive test under both treatments once at the start (pre) and at the end (post).
My advisor has now suggested calculating an ANCOVA since the pre-values differ between the two treatments. To do this, I tried to do the following:
- Open Repeated Measures ANOVA
- Add both treatments as levels of RM factor 1
- Add both post-measurements as outcome variables (repeated measures cells)
- Add both pre-measurements as covariates
Is this correct? I am not sure if this is correct, since here, the pre-measurement of treatment A would also serve as a covariate for the post-measurement of treatment B (and the other way around). This sounds like a problem to me, but I am not sure...
So basically, my question is: Is it possible to do an ANCOVA in a pre-post within-subjects design with the pre-measurement as a covariate?
Thank you in advance!