Okay, so I have a problem with repeated measurements ANOVA.
I'm doing my thesis, and the research I'm doing is basically as follows:
50 participants have gone a shoulder arthroscopy and they have done 2 month rehabilitation program. At 2 months, they all do shoulder test (scale 0-100). After this, they are randomized to 2 groups: intervention (accelerated rehab program) and usual rehabilitation group (the same program which they have already been doing). The shoulder test is repeated at 6 months and 12 months follow up. I should notify, that they all also performed the shoulder test before the arthroscopy (preoperative).
Now, I should test if there is difference within and between the groups during that 12 month span. I performed repeated measurements ANOVA and everything is great. However, my professor wants me to use baseline values (shoulder test scores before the intervention and after the arthroscopy (done 2 months after arthroscopy)) as covariate.
How should I do this? Do I put 6 month and 12 month shoulder test scores in to the 'Within-subject variables" and 2 month shoulder test scores to covariate?
If so, how do I calculate 2 month shoulder test score for the table? Do I run repeated mesurements ANOVA again with 2 month shoulder test score placed in 'Within-subject variables" and check the values there or do I run other t-test perhaps?