Research questions regarding how, for whom, and where a treatment achieves its effect on an outcome have become increasingly valued in substantive research. Such questions can be answered by causal moderated mediation analysis, which assesses the heterogeneity of the mediation mechanism underlying the treatment effect across individual and…

This monograph critiques the many nonexperimental impact estimation approaches that have been based on external comparison groups. It proposes an approach to evaluating employment and training (E&T) programs that calls for using the group of individuals who apply to a program but then choose not to participate in that program as an…