Generalizing Difference-in-Differences to Non-Canonical Settings: Identifying an Array of Estimands
将双重差分推广至非典型情形:识别多种因果估计对象
Consider a general setting in which data on an outcome is collected in two `groups' at two time periods, with certain group-periods deemed `treated' and others `untreated'. A special case is the canonical Difference-in-Differences (DiD) setting in which one group is treated only in the second period while the other is treated in neither period. Then it is well known that under a parallel trends assumption across the two groups the classic DiD formula (subtracting the average…