[gov3009-l] VanderWeele on "Mediation and spillover effects in group-randomized trials"

Hello all, We hope you will join us this Wednesday, February 10th at the Applied Statistics workshop when we will be happy to have Tyler VanderWeele (Harvard School of Public Health). Details and an abstract are below. A light lunch will be served. Thanks! "Mediation and spillover effects in group-randomized trials: a case study of the 4R's educational intervention." Tyler VanderWeele Department of Epidemiology and Biostatistics Harvard School of Public Health February 10th, 2010, 12 noon K354 CGIS Knafel (1737 Cambridge St) ABSTRACT: In many group-randomized trials, questions of mediation are of interest. In the education setting, often the treatment is at the school level, the mediator is at the classroom level and the outcome is at the individual level. The standard approach to mediation analysis in the social sciences is subject to three important shortcoming: (1) failure to account for possible treatment-mediator interaction, (2) failure to account for mediator-outcome confounding (even if the treatment is randomized the mediator is not and is thus subject to selection-confounding issues) and (3) failure to account for the spillover effects of one classroom on the outcomes of children in other classroom. Ignoring any of these three issues can lead to biases and misleading inferences. Using a counterfactual conceptualization of direct, indirect and spillover effects, we provide a framework that can accommodate all three of these issues. We show that the total effect can be decomposed into what is defined as a natural direct effect, a within-classroom mediated effect and a spillover mediated effect. We give identification conditions for each of the causal effects of interest and we provide theoretical results on the sequences of ignoring "interference" or spillover effects when they are in fact present. The methodology is applied to a group-randomized trial of the 4R's educational intervention. Cheers, matt. ~~~~~~~~~~~ Matthew Blackwell PhD Candidate Institute for Quantitative Social Science Department of Government Harvard University email: mblackwell(a)iq.harvard.edu url: http://people.fas.harvard.edu/~blackwel/