Evaluating Preschool Programs When Length of Exposure to the Program Varies: A Nonparametric Approach
利用非实验数据评估玻利维亚学前教育项目对认知、心理社会和人体测量结果的影响，发现影响高度依赖年龄和暴露时长，并开发了广义匹配估计量来控制选择性偏差。
Nonexperimental data are used to evaluate impacts of a Bolivian preschool program on cognitive, psychosocial, and anthropometric outcomes. Impacts are shown to be highly dependent on age and exposure duration. To minimize the effect of distributional assumptions, program impacts are estimated as nonparametric functions of age and duration. A generalized matching estimator is developed and used to control for nonrandom selectivity into the program and into exposure durations. Comparisons with three groups-children in the feeder area not in the program, children in the program for ≤ 1 month, and children living in similar areas without the program-indicate that estimates are robust for significant positive effects of the program on cognitive and psychosocial outcomes with ≥ 7 months' exposure, although the age patterns of effects differ slightly by comparison group. 2004 President and Fellows of Harvard College and the Massachusetts Institute of Technology.