We provide simple tests for selection on unobserved variables in the Vytlacil-Imbens-Angrist framework for Local Average Treatment Effects. The tests allow researchers not only to test for selection on either or both of the treated and untreated outcomes, but also to assess the magnitude of the...

Workers acquire skills through formal schooling, through training provided by governments, and through training provided by firms. This chapter reviews, synthesizes, and augments the literature on the last of these, which has languished in recent years despite the sizable contribution of firm...