The Effect of High-Tech Clusters on the Productivity of Top Inventors: Comment
本文评论了Moretti（2021）关于技术集群规模与专利产出之间正向弹性的研究，指出其事件研究未利用发明人跨城市流动的变异，且工具变量因编码错误而构建有误。作者修正后得到零效应，认为原报告的弹性可能非因果关系。
Moretti (2021) reports a positive elasticity between technology cluster size and patenting, and uses an event study and instrumental variables regressions to justify a causal interpretation. The event study does not use the variation generated by inventors moving across cities, and the instrument is constructed incorrectly due to a coding error. I run a corrected event study and fix the coding error, and find null effects. The reported elasticity may not be causal.