Difference-in-Differences Estimators of Intertemporal Treatment Effects
研究了面板数据中非二元、非吸收性处理的跨期效应估计，提出事件研究估计量和归一化估计量，并指出双向固定效应回归在异质性处理效应下存在偏误。
Abstract We study treatment-effect estimation using panel data. The treatment may be non-binary, non-absorbing, and the outcome may be affected by treatment lags. We make a parallel-trends assumption, and propose event-study estimators of the effect of being exposed to a weakly higher treatment dose for ℓ. periods. We also propose normalized estimators, that estimate a weighted average of the effects of the current treatment and its lags. We also analyze commonly-used two-way-fixed-effects regressions. Unlike our estimators, they can be biased in the presence of heterogeneous treatment effects. A local-projection version of those regressions is biased even with homogeneous effects.