Direct and Indirect Effects

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 prac­ tical difficulties (in nonlinear models), be­ cause they cannot be isolated by holding cer­ tain variables constant. This paper presents a new way of defining the effect transmit­ ted through a restricted set of paths, without controlling variables on the remaining paths. This permits the assessment of a more nat­ ural 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 con­ ditions under which such assessments can be estimated consistently from experimen­ tal and nonexperimental data, and thus ex­ tends path-analytic techniques to nonlinear and nonparametric models.