What Can Ex-Participants Reveal about a Program’s Impact?
提出一种三重差分法，在无法进行干预前基线调查但能追踪前参与者时，估计社会项目的平均影响，并应用于阿根廷工作福利项目，发现对参与者当前收入有显著影响。
We propose a method for estimating the mean impact of an assigned social program when it is not feasible to do a pre-intervention baseline survey but it is feasible to track ex-participants. In our triple-difference estimator, measured outcome changes are compared between continuing participants and matched ex-participants, after netting out the outcome changes for a matched comparison group who never participated. With sufficient followup observations one can test the joint conditions required for correctly identifying the gains to current participants. We apply the method to a workfare program in Argentina. Significant impacts on participants’ current incomes are revealed.