title: Principal stratification--uses and limitations.
abstract: Pearl (2011) asked for the causal inference community to clarify the role of the principal stratification framework in the analysis of causal effects. Here, I argue that the notion of principal stratification has shed light on problems of non-compliance, censoring-by-death, and the analysis of post-infection outcomes; that it may be of use in considering problems of surrogacy but further development is needed; that it is of some use in assessing "direct effects"; but that it is not the appropriate tool for assessing "mediation." There is nothing within the principal stratification framework that corresponds to a measure of an "indirect" or "mediated" effect.
authors.affiliation: Harvard University, USA.
authors.forename: Tyler J
authors.initials: TJ
authors.lastname: Vanderweele
mesh_terms: D015984:Causality; D015233:Models, Statistical