I have a question about including a random intercept per subject in a mixed model and using a autoregressive covariance structure.
I have longitudinal data with repeated measures per subject (observational study). A statistician told me that I should not include a random intercept per subject in a model when I use a autoregressive covariance structure (AR(1)), since using this covariance structure you already account for differences between observations of people. I don't really understand why?
Should I furthermore include baseline outcome in my mixed model to correct for it?
Hopefully someone can help me.