Variants of double robust estimators for two-stage dynamic treatment regimes

Certain conditions and illnesses may necessitate multiple stages of treatment and thus require unique study designs to compare the efficacy of these interventions. Such studies are characterized by two or more stages of treatment punctuated by decision points where intermediate outcomes inform the choice for the next stage of treatment. The algorithm that dictates what treatments to take based on intermediate outcomes is referred to as a dynamic regime. This paper describes an efficient method of building double robust estimators of the treatment effect of different regimes. A double robust estimator utilizes both modeling of the outcome and weighting based on the modeled probability of receiving treatment in such a way that the resulting estimator is a consistent estimate of the desired population parameter under the condition that at least one of those models is correct. This new and more efficient double robust estimator is compared to another double robust estimator as well as classical regression and inverse probability weighted estimators. The methods are applied to estimate the regime effects in the STAR*D anti-depression treatment trial.