A1316
Title: Causal mediation with instrumental variables
Authors: Kara Rudolph - Columbia University (United States) [presenting]
Ivan Diaz - NYU Langone Health (United States)
Nicholas Williams - Columbia University (United States)
Abstract: Mediation analysis is a strategy for understanding the mechanisms by which interventions affect later outcomes. However, unobserved confounding concerns may be compounded in mediation analyses, as there may be unobserved exposure-outcome, exposure-mediator, and mediator-outcome confounders. Instrumental variables (IVs) are a popular identification strategy in the presence of unobserved confounding. However, in contrast to the rich literature on the use of IV methods to identify and estimate a total effect of a non-randomized exposure, there has been almost no research into using IV as an identification strategy to identify mediational indirect effects. In response, novel estimands are defined and nonparametrically identified -complier interventional direct and indirect effects---when two, possibly related, IVs are available, one for the exposure and another for the mediator. Nonparametric, robust, efficient estimators are proposed for these effects and related compiler natural direct and indirect effects, and they are applied to a housing voucher experiment.
