Natural and Quasi-Experiments in Economics
介绍经济学中模仿随机实验的研究设计，利用外生变动（如法律变化、征兵机制）来获得可检验的因果推断，并讨论如何改进这些方法及判断其结论的有效性。
Abstract Using research designs patterned after randomized experiments, many recent economic studies examine outcome measures for treatment groups and comparison groups that are not randomly assigned. By using variation in explanatory variables generated by changes in state laws, government draft mechanisms, or other means, these studies obtain variation that is readily examined and is plausibly exogenous. This article describes the advantages of these studies and suggests how they can be improved. It also provides aids in judging the validity of inferences that they draw. Design complications such as multiple treatment and comparison groups and multiple preintervention or postintervention observations are advocated. KEY WORDS: Comparison groupsControl groupsDifference in differencesExogeneityExperimental designObservational studies