Synthetic Control under Out-of-Span Common Shocks: Diagnosis, Exposure Balance and Correction
跨度之外共同冲击下的合成控制:诊断、暴露平衡与修正
Synthetic control relies on pre-treatment fit to balance the unobserved factors that drive untreated outcomes. The argument fails when an observed common shock, such as a commodity price, moves with the latent factors before treatment and departs from them afterwards and pre-treatment fit then says almost nothing about the synthetic unit's exposure to the shock. I derive a period-specific bound that links the post-treatment bias of any weighting estimator to pre-treatment…