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Generalized causal mediation analysis.

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Biometrics

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      Abstract

      The goal of mediation analysis is to assess direct and indirect effects of a treatment or exposure on an outcome. More generally, we may be interested in the context of a causal model as characterized by a directed acyclic graph (DAG), where mediation via a specific path from exposure to outcome may involve an arbitrary number of links (or "stages"). Methods for estimating mediation (or pathway) effects are available for a continuous outcome and a continuous mediator related via a linear model, while for a categorical outcome or categorical mediator, methods are usually limited to two-stage mediation. We present a method applicable to multiple stages of mediation and mixed variable types using generalized linear models. We define pathway effects using a potential outcomes framework and present a general formula that provides the effect of exposure through any specified pathway. Some pathway effects are nonidentifiable and their estimation requires an assumption regarding the correlation between counterfactuals. We provide a sensitivity analysis to assess the impact of this assumption. Confidence intervals for pathway effect estimates are obtained via a bootstrap method. The method is applied to a cohort study of dental caries in very low birth weight adolescents. A simulation study demonstrates low bias of pathway effect estimators and close-to-nominal coverage rates of confidence intervals. We also find low sensitivity to the counterfactual correlation in most scenarios.

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      Author and article information

      Affiliations
      [1 ] Department of Epidemiology and Biostatistics, School of Medicine, WG-43, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA. jma13@case.edu
      Journal
      Biometrics
      Biometrics
      1541-0420
      0006-341X
      Sep 2011
      : 67
      : 3
      10.1111/j.1541-0420.2010.01547.x
      21306353
      3139764
      NIHMS260919
      © 2011, The International Biometric Society.

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