Bartik Instruments: What, When, Why, and How
解释了Bartik工具变量的构造原理，指出其本质是暴露研究设计，并展示了如何评估该研究设计的合理性，通过劳动供给弹性和移民与本地人替代弹性的两个应用加以说明。
The Bartik instrument is formed by interacting local industry shares and national industry growth rates. We show that the typical use of a Bartik instrument assumes a pooled exposure research design, where the shares measure differential exposure to common shocks, and identification is based on exogeneity of the shares. Next, we show how the Bartik instrument weights each of the exposure designs. Finally, we discuss how to assess the plausibility of the research design. We illustrate our results through two applications: estimating the elasticity of labor supply, and estimating the elasticity of substitution between immigrants and natives.