Standard Synthetic Control Methods: The Case of Using All Preintervention Outcomes Together With Covariates
标准合成控制：同时使用全部干预前结果与协变量的情形
It is becoming increasingly popular in applications of standard synthetic control methods to include the entire pretreatment path of the outcome variable as economic predictors. We demonstrate both theoretically and empirically that using all outcome lags as separate predictors renders all other covariates irrelevant in such settings. This finding holds irrespective of how important these covariates are for accurately predicting posttreatment values of the outcome,…