Before revision: This paper studies identification of program effects in settings with latent choice sets. Here, by latent choice sets, I mean the unobserved heterogeneity that arises when the choice set from which the agent selects treatment is heterogeneous and unobserved by the researcher . The analysis is developed in the context of the Head Start Impact Study, a social experiment designed to evaluate preschools as part of Head Start, the largest early childhood education program in the United States .
After revision: In a common experimental format, individuals are randomly assigned to either a treatment group with program access or a control group without access. In such experiments, analyzing the average effects of the treatment of program access may be hindered by the largest early childhood education program in the United States .