论文标题
平行趋势在事件研究环境中的作用：环境经济学的应用
The role of parallel trends in event study settings: An application to environmental economics
论文作者
论文摘要
差异差异（DID）研究设计通常依赖于治疗时机的变化，以便在做出适当的平行趋势假设后，可以识别，估计和推断因果关系。但是，实际上，不同的程序依赖于不同的平行趋势假设（PTA），并恢复了不同的因果参数。在本文中，我们专注于交错的DID（也称为事件研究），并讨论了PTA在因果参数的识别和估计方面所起的作用。我们在基础PTA的实力方面记录了``鲁棒性''与``效率''的权衡，并认为在使用DID程序时，从业者应明确这些权衡。我们提出了反映这些权衡并得出其较大样本属性的新DID估计器。我们通过评估从联邦政府到《清洁水法》管理的过渡是否影响合规率来说明这些结果的实际相关性。
Difference-in-Differences (DID) research designs usually rely on variation of treatment timing such that, after making an appropriate parallel trends assumption, one can identify, estimate, and make inference about causal effects. In practice, however, different DID procedures rely on different parallel trends assumptions (PTA), and recover different causal parameters. In this paper, we focus on staggered DID (also referred as event-studies) and discuss the role played by the PTA in terms of identification and estimation of causal parameters. We document a ``robustness'' vs. ``efficiency'' trade-off in terms of the strength of the underlying PTA, and argue that practitioners should be explicit about these trade-offs whenever using DID procedures. We propose new DID estimators that reflect these trade-offs and derived their large sample properties. We illustrate the practical relevance of these results by assessing whether the transition from federal to state management of the Clean Water Act affects compliance rates.
