Interpretation and Identification of Causal Mediation

Psychological Methods, Forthcoming

45 Pages Posted: 25 Oct 2013

See all articles by Judea Pearl

Judea Pearl

University of California, Los Angeles (UCLA) - Computer Science Department

Date Written: September 18, 2013


This paper reviews the foundations of causal mediation analysis and offers a general and transparent account of the conditions necessary for the identification of natural direct and indirect effects, thus facilitating a more informed judgment of the plausibility of these conditions in specific applications. We show that the conditions usually cited in the literature are overly restricted, and can be relaxed substantially, without compromising identification. In particular, we show that natural effects can be identified by methods that go beyond standard adjustment for confounders, applicable to observational studies in which treatment assignment remains confounded with the mediator or with the outcome. These identification conditions can be validated algorithmically from the diagramatic description of one's model, and are guaranteed to produce unbiased results whenever the description is correct. The identification conditions can be further relaxed in parametric models, possibly including interactions, and permit us to compare the relative importance of several pathways, mediated by interdependent variables.

Suggested Citation

Pearl, Judea, Interpretation and Identification of Causal Mediation (September 18, 2013). Psychological Methods, Forthcoming, Available at SSRN:

Judea Pearl (Contact Author)

University of California, Los Angeles (UCLA) - Computer Science Department ( email )

4732 Boelter Hall
Los Angeles, CA 90095
United States


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