Two-way fixed effects and differences-in-differences with heterogeneous treatment effects: a survey
综述了当政策效果在不同群体或时间点存在差异时，双向固定效应回归可能产生误导性估计的问题，并介绍了稳健的替代估计方法，最后用这些方法重新审视了Wolfers（2006a）的研究。
Summary Linear regressions with period and group fixed effects are widely used to estimate policie’s effects: 26 of the 100 most cited papers published by the American Economic Review from 2015 to 2019 estimate such regressions. It has recently been shown that those regressions may produce misleading estimates if the policy’s effect is heterogeneous between groups or over time, as is often the case. This survey reviews a fast-growing literature that documents this issue and that proposes alternative estimators robust to heterogeneous effects. We use those alternative estimators to revisit Wolfers (2006a).