The concepts of principal strata direct and indirect effects are compared with and contrasted to definitions of direct and indirect effects which make reference to interventions on intermediate variables. Certain simple relations hold for direct effects but not indirect effects.

In the presence of interference, the exposure of one individual may affect the outcomes of others. We provide new effect partitioning results under interferences that express the overall effect as a sum of (i) the indirect (or spillover) effect and (ii) a contrast between two direct effects.