Substitution and Dropout Bias in Social Experiments: A Study of an Influential Social Experiment
探讨社会实验中，对照组使用替代方案和治疗组退出实验导致的偏差，利用课堂培训项目数据证明其重要性，并指出实验证据常被误读。
This paper considers the interpretation of evidence from social experiments when persons randomized out of a program being evaluated have good substitutes for it, and when persons randomized into a program drop out to pursue better alternatives. Using data from an experimental evaluation of a classroom training program, we document the empirical importance of control group substitution and treatment group dropping out. Evidence that one program is ineffective relative to close substitutes is not evidence that the type of service provided by all of the programs is ineffective, although that is the way experimental evidence is often interpreted.