An Interventionist Approach to Mediation Analysis
James M. Robins, Thomas S. Richardson, and Ilya Shpitser

TL;DR
This paper develops a new interventionist framework for mediation analysis that avoids cross-world counterfactuals, clarifies identification conditions, and enhances empirical testability of causal mediation effects.
Contribution
It introduces a self-contained interventionist approach to mediation, linking it with path-specific effects and providing an algorithm for identification.
Findings
The framework is empirically testable in randomized trials.
Identification is possible except in cases with a recanting witness.
The approach unifies interventionist and counterfactual theories under certain conditions.
Abstract
Judea Pearl's insight that, when errors are assumed independent, the Pure (aka Natural) Direct Effect (PDE) is non-parametrically identified via the Mediation Formula was `path-breaking' in more than one sense! In the same paper Pearl described a thought-experiment as a way to motivate the PDE. Analysis of this experiment led Robins \& Richardson to a novel way of conceptualizing direct effects in terms of interventions on an expanded graph in which treatment is decomposed into multiple separable components. We further develop this novel theory here, showing that it provides a self-contained framework for discussing mediation without reference to cross-world (nested) counterfactuals or interventions on the mediator. The theory preserves the dictum `no causation without manipulation' and makes questions of mediation empirically testable in future Randomized Controlled Trials. Even so, we…
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Taxonomy
TopicsPsychotherapy Techniques and Applications · Qualitative Comparative Analysis Research · Philosophy and History of Science
