Statistics Colloquium : Dr. Elizabeth Stuart

Title: Sensitivity analyses for unobserved effect moderation when generalizing from trial to population

Abstract: In the presence of treatment effect heterogeneity, the average treatment effect (ATE) in a randomized controlled trial (RCT) may differ from the average effect of the same treatment if applied to a target population of interest.  But for policy purposes we may desire an estimate of the target population ATE. If all treatment effect moderators are observed in the RCT and in a data set representing the target population, then we can obtain an estimate for the target population ATE by adjusting for the difference in the distribution of the moderators between the two samples. However, that is often an unrealistic assumption in practice. This talk will discuss methods for generalizing treatment effects under that assumption, as well as sensitivity analyses for two situations: (1) where we cannot adjust for a specific moderator observed in the RCT because we do not observe it in the target population; and (2) where we are concerned that the treatment effect may be moderated by factors not observed even in the RCT.  Outcome-model and weighting-based sensitivity analysis methods are presented. The methods are applied to examples in drug abuse treatment. Implications for study design and analyses are also discussed, when interest is in a target population ATE.