The scenario is regarding treatment effect in an observational study (i.e. not randomised): those given the treatment would be more unwell at baseline.
A clinical trials statistician suggested adding in the baseline as a covariate in the regression model. I remember this being acceptable in randomised trials (RCT), but not observational studies (where propensity scores are commonly used).
Can someone please explain:
1) why adding baseline as covariate is not statistically acceptable in observational studies but is in RCTs
2) what other methods are there in addition to PS?