Causal organic indirect and direct effects: closer to Baron and Kenny, with a product method for binary mediators

Understand

Mediation analysis, which started with Baron and Kenny (1986), is used extensively by applied researchers.

• Indirect and direct effects are the part of a treatment effect that is mediated by a covariate and the part that is not.
• Subsequent work on natural indirect and direct effects provides a formal causal interpretation, based on cross-worlds counterfactuals: outcomes under treatment with the mediator set to its value without treatment.
• Organic indirect and direct effects (Lok 2016) avoid cross-worlds counterfactuals, using so-called organic interventions on the mediator while keeping the initial treatment fixed at treatment.