I have two groups of patients, those with (OSA) and those without (nOSA) sleep apnoea. Patients were scheduled to undergo a surgical procedure (Sx). Each patient completed a type of quality of life survey before (pre-Sx) and after (post-Sx) surgery. Each question in the quality of life survey is scored 0, 1, 2, 3 (with 0 being the "best" and 3 being the "worst").
I want to find answer a specific question, but am unsure which test is most appropriate - Was the change in quality of life (change in the ordinal variable) following the surgery different for OSA versus nOSA patients? We suspect that the OSA group has a greater change in quality of life after surgery, compared with the nOSA group.
So I need some kind of test which can compare the change in the distribution of the scores between the two groups?
Or would it make sense to some kind of multivariate analysis and use "OSA/nOSA" as a variable and see if it significantly contributes to the change in quality of life after surgery. Could I do a multivariate regression model of some kind?
Any insights most welcome!