Direct and Indirect Effects

TLDR

Direct effects are defined by holding intermediate variables constant, while indirect effects are difficult to isolate in nonlinear models because they cannot be obtained by holding certain variables constant. The study introduces a new definition of effects transmitted through a restricted set of paths without controlling variables on the remaining paths. The authors establish conditions that allow consistent estimation of these effects from experimental and nonexperimental data, extending path‑analytic techniques to nonlinear and nonparametric models. This approach enables assessment of more natural direct and indirect effects applicable to both linear and nonlinear models, offering broader policy‑related interpretations.

Abstract

The direct effect of one event on another can be defined and measured by holding constant all intermediate variables between the two. Indirect effects present conceptual and practical difficulties (in nonlinear models), because they cannot be isolated by holding certain variables constant. This paper presents a new way of defining the effect transmitted through a restricted set of paths, without controlling variables on the remaining paths. This permits the assessment of a more natural type of direct and indirect effects, one that is applicable in both linear and nonlinear models and that has broader policy-related interpretations. The paper establishes conditions under which such assessments can be estimated consistently from experimental and nonexperimental data, and thus extends path-analytic techniques to nonlinear and nonparametric models.