On the causal interpretation of randomised interventional indirect effects

Journal of the Royal Statistical Society: Series B (Statistical Methodology) · 2023 · Volume 85 · Issue 4

Abstract

Identification of standard mediated effects such as the natural indirect effect relies on heavy causal assumptions. By circumventing such assumptions, so-called randomised interventional indirect effects have gained popularity in the mediation literature. Here, I introduce properties one might demand of an indirect effect measure in order for it to have a true mediational interpretation. For instance, the sharp null criterion requires an indirect effect measure to be null whenever no individual-level indirect effect exists. I show that without stronger assumptions, randomised interventional indirect effects do not satisfy such criteria. I additionally discuss alternative causal interpretations of such effects.

Keywords

cross-world counterfactual independence, HIV/AIDS, identification, mediation, stochastic intervention, time-varying confounding

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