论文标题
选择和平行趋势
Selection and parallel trends
论文作者
论文摘要
我们研究选择在治疗中的作用在差异差异（DID）设计中的作用。我们为一般选择机制的一般类别的假设提供了必要和充分的条件。这些条件表征了并行趋势的经验内容。我们使用必要的条件来提供基于选择的DID偏差分解，并提供易于实施的策略来对其组件进行基准测试。我们还为在有或没有协变量的应用中提供了用于合理性的模板。对新南威尔士州培训计划的因果效应的重新分析证明了我们基于选择的方法对DIT的偏见进行基准测试的有用性。
We study the role of selection into treatment in difference-in-differences (DiD) designs. We derive necessary and sufficient conditions for parallel trends assumptions under general classes of selection mechanisms. These conditions characterize the empirical content of parallel trends. We use the necessary conditions to provide a selection-based decomposition of the bias of DiD and provide easy-to-implement strategies for benchmarking its components. We also provide templates for justifying DiD in applications with and without covariates. A reanalysis of the causal effect of NSW training programs demonstrates the usefulness of our selection-based approach to benchmarking the bias of DiD.
