Many studies use shift-share (or “Bartik”) instruments, which average a set of shocks with exposure share weights. We provide a new econometric framework for shift-share instrumental variable (SSIV) regressions in which identification follows from the quasi-random assignment of shocks, while exposure shares are allowed to be endogenous. The framework is motivated by an equivalence result: the orthogonality between a shift-share instrument and an unobserved residual can be represented as the orthogonality between the underlying shocks and a shock-level unobservable. SSIV regression coefficients can similarly be obtained from an equivalent shock-level regression, motivating shock-level conditions for their consistency. We discuss and illustrate several practical insights of this framework in the setting of Autor et al. (2013), estimating the effect of Chinese import competition on manufacturing employment across U.S. commuting zones.

中文翻译：

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准实验转移共享研究设计

许多研究使用转移份额（或“Bartik”）工具，通过暴露份额权重对一组冲击进行平均。我们为转变份额工具变量（SSIV）回归提供了一个新的计量经济学框架，其中识别来自于冲击的准随机分配，而风险份额允许是内生的。该框架的动机是等效结果：移位份额工具和不可观察残差之间的正交性可以表示为潜在冲击和不可观察冲击水平之间的正交性。SSIV 回归系数可以类似地从等效冲击水平回归中获得，从而激发冲击水平条件的一致性。我们在 Autor 等人的背景下讨论并说明了该框架的几个实际见解。(2013),