Path-Specific Effects

Abstract

A cause may influence its effect via multiple paths. Paradigmatically (Hesslow, 1974), taking birth control pills both decreases one's risk of thrombosis by preventing pregnancy and increases it by producing a blood chemical. Building on Pearl (2001), I explicate the notion of a path-specific effect. Roughly, a path-specific effect of C on E via path P is the degree to which a change in C would change E were they to be transmitted only via P. Facts about such effects may be gleaned from the structural equations commonly used to represent the causal relationships among variables. I contrast my analysis of the Hesslow case with those given by theorists of probabilistic causality, who mistakenly link it to issues of causal heterogeneity, token-causation and indeterminism. The reason probabilistic theories misdiagnose this case is that they pay inadequate attention to the structural relationships among variables.

Signal Manipulation and the Causal Analysis of Racial Discrimination

“…This resulting causal model contains the path C ® S ® Y. In such a model, one could determine the effect of C on Y via a signal manipulation of S. The ability to do so is at the center of causal mediation techniques (Imai, Keele, & Tingley 2010;Pearl 2001), which measure the way that an effect variable would respond to a change in a cause variable, were that change to be transmitted via some causal paths but not others (Weinberger 2019). For models with multiple paths between the cause and effect, the definitions for the various effects along the different paths (e.g., direct and indirect effects) can become somewhat involved.…”