The October 7th, 2016 Workshop on Quantitative Methods in Education, Health, and the Social Sciences (QMeHSS) will take place from 10:30am - 12:00pm in NORC Conference room 344. Xu Qin and Dr. Guanglei Hong from the University of Chicago will be leading our inagurial workshop for the 2016-2017 academic year. NORC is located at 1155 E. 60th Street.
Assessing Heterogeneity of Causal Mediation Mechanism in Multi-Site Trials
PhD Student, Comparative Human Development Department, University of Chicago
Associate Professor, Comparative Human Development Department, Committee on Education, University of Chicago
In multi-site trials, when an intervention delivered within each site displays uneven impacts across sites, it becomes necessary to further investigate heterogeneous mediation mechanisms. We incorporate a theoretical model of multi-site causal mediation process in the potential outcomes causal framework and conceptualize between-site heterogeneity in the mediation mechanism as novel causal parameters of theoretical interests. We identify not only the population average but also the between-site variance of causal mechanisms, through a novel propensity score based weighting approach. A method-of-moments procedure is proposed to consistently estimate the causal parameters. We derive asymptotic standard errors that reflect the sampling variability of the estimated weight. Unlike most mediation analyses based on path analysis and structural equation modeling in psychological studies, the strategy addresses the influence of confounding variables, conveniently relaxes the assumption of no treatment-by-mediator interaction, and thus enhances causal inference. In the meantime, it simplifies the outcome model specification without invoking strong distributional assumptions. Simulations display satisfactory performance of the proposed method.