483 – GSS/SSS/SRMS Student Paper Award Presentations
Analyzing Heterogeneous Causal Mediation Effects in Multi-Site Trials with Application to the National Job Corps Study
Xu Qin
University of Chicago
Guanglei Hong
The University of Chicago
When a multi-site randomized trial reveals between-site variation in program impact, methods are needed for further investigating heterogeneous mediaton mechanisms across the sites. We conceptualize and identify a joint distribution of site-specific direct and indirect effects under the potential outcomes framework. A method-of-moments procedure incorporating ratio-of-mediator-probability weighting (RMPW) consistently estimates the causal parameters. This strategy conveniently relaxes the assumption of no treatment-by-mediator interaction while greatly simplifying the outcome model specification without invoking strong distributional assumptions. We derive asymptotic standard errors that reflect the sampling variability of the estimated weight.