Design-based Analysis in Difference-In-Differences Settings with Staggered Adoption
研究了面板数据中交错采用政策或处理时，平均处理效应的估计与推断问题，证明在随机分配采用时间下，标准双重差分估计量是特定加权平均因果效应的无偏估计，且标准方差估计量是保守的。
In this paper we study estimation of and inference for average treatment effects in a setting with panel data. We focus on the setting where units, e.g., individuals, firms, or states, adopt the policy or treatment of interest at a particular point in time, and then remain exposed to this treatment at all times afterwards. We take a design perspective where we investigate the properties of estimators and procedures given assumptions on the assignment process. We show that under random assignment of the adoption date the standard Difference-In-Differences estimator is is an unbiased estimator of a particular weighted average causal effect. We characterize the proeperties of this estimand, and show that the standard variance estimator is conservative.