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Title: Mediation analysis with external summary data on total effect Authors:  Bhramar Mukherjee - University of Michigan (United States) [presenting]
Abstract: As modern assaying technologies continue to improve, environmental health studies are increasingly measuring endogenous omics data to study intermediary biological pathways of outcome-exposure associations. Mediation analysis is often carried out when there is well-established literature showing the statistical and practical significance of the association between an exogenous exposure and a health outcome of interest, or the total effect. For example, there are a plethora of studies associating maternal phthalate exposure with preterm delivery, and researchers are now trying to characterize the mechanisms by which phthalate exposure impacts final gestational age. The existing methodology for performing mediation analyses does not leverage the rich external information available on the total effect. We show that incorporating external summary-level information on the total effect improves the estimation efficiency of the natural direct and indirect effects, and is a function of the partial R-squared comparing the outcome model with and without the mediators. Additionally, we discuss how to handle incongruous external information which can arise from transportability violations or fundamentally different adjustment sets. The proposed framework blends mediation analysis with modern data integration techniques.