Since results from MDRC's longitudinal, random-assignment evaluation of career-academy high schools revealed that several years after high-school completion, those randomized to receive the academy opportunity realized a $175 (11 percent) increase in monthly earnings, on average, the current study examined the impact of duration of actual academy enrollment, because nearly half of treatment group students either never enrolled or participated for only a portion of high school.
Based on data from the experimental evaluation, the current study used a principal stratification framework and Bayesian inference to investigate the causal impact of academy participation. The analysis focused on a sample of 1,306 students across seven sites in the MDRC evaluation. Participation was measured by number of years of academy enrollment, and the outcome of interest was average monthly earnings in the period of four to eight years after high school graduation. The study estimated an average causal effect of treatment assignment on subsequent monthly earnings of approximately $588 among males who remained enrolled in an academy throughout high school and more modest impacts among those who participated only partially. Different from an instrumental variables approach to treatment non-compliance, which allows for the estimation of linear returns to treatment take-up, the more general framework of principal stratification allows for the consideration of non-linear returns, although at the expense of additional model-based assumptions. (publisher abstract modified)