Bounds on Treatment Effects in the Presence of Sample Selection and Noncompliance: The Wage Effects of Job Corps∗

Randomized and natural experiments are commonly used in economics and other social science fields to estimate the effect of programs and interventions. Even when employing experimental data, assessing the impact of the treatment on outcomes of interest is often complicated by the presence of sample selection (outcomes are only observed for a selected group) and noncompliance with the assigned treatment (some treatment group individuals do not receive the treatment while some control individuals do). We address both of these identification problems simultaneously and derive nonparametric bounds for average treatment effects within a principal stratification framework. We employ these bounds to empirically assess the wage effects of the Job Corps (JC) program, which is the most comprehensive and largest federally-funded job training program for disadvantaged youth in the United States. Our results strongly suggest positive average effects of JC on wages for individuals who comply with their treatment assignment and would be employed whether or not they enrolled in JC (the “always-employed compliers”). In particular, under relatively weak monotonicity and mean dominance assumptions, we find that this average effect is between 5.7 and 13.9 percent four years after randomization, and between 7.7 and 17.5 percent for Non-Hispanics.