Estimation of the Optimal Time to Start Antiretroviral Therapy in HIV Infected Patients using Dynamic Regime Marginal Structural Models

I present a method for estimating, from observational cohort data, the optimal CD4 count (and/or HIV RNA level) x at which to start HAART within a grace period of t months. The method is based on dynamic regime marginal structural models . Specifically I consider the set of regimes: start HAART within t months of the first time a subjects CD4 falls below x. Clinically enforceable regimes require a grace period t of at least 2-3 months. I consider the implications of our results for the clinical interpretation of various analyses that have been appeared in the published literature.