text: 393,71,1006699758755426304,2935607927,Peter Hull,"New(ish) working paper with Kirill Borusyak and Xavier Jaravel: ""Quasi-experimental Shift-share Research Designs""  <LINK> Comments very welcome! A brief summary thread follows <LINK> This paper updates a May 2017 note on how to think about identification in ""shift-share"" or ""Bartik"" IVs as coming from quasi-random variation in the aggregate shocks  Although this seems to often be the intuition behind shift-share IV, we haven't yet seen it formalized <LINK> We first show that even though Bartik IV is estimated in the ""location"" space, its validity condition can be expressed in the ""industry"" space (i.e. the space of shocks g).  For shift-share IV validity, the covariance of g and relevant unobservables should be close to zero. <LINK> We then derive sufficient shock-level assumptions for this condition to hold. We think of shocks as being as-good-as-randomly assigned, with the impact of each shock shrinking as the sample grows We also consider extensions with conditionally random shocks and panel variation <LINK> Lastly we caution that estimating aggregate shocks in the IV sample can make shift-share IV inconsistent, even when the shocks are random  This probably is analogous to the classic inconsistency of many-instrument 2SLS and can similarly be solved by split-sample shock estimation <LINK> We hope this helps clarify how one may think of identification in shift-share IVs as ""coming from"" a natural shock experiment, and conclude with some practical advice for such settings Of course this is work in progress, so its helpfulness is up to you! Please send your thoughts",https://arxiv.org/abs/1806.01221,"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. ",Quasi-Experimental Shift-Share Research Designs,6,"['New(ish) working paper with Kirill Borusyak and Xavier Jaravel: ""Quasi-experimental Shift-share Research Designs"" \n\n<LINK>\n\nComments very welcome! A brief summary thread follows <LINK>', 'This paper updates a May 2017 note on how to think about identification in ""shift-share"" or ""Bartik"" IVs as coming from quasi-random variation in the aggregate shocks \n\nAlthough this seems to often be the intuition behind shift-share IV, we haven\'t yet seen it formalized https://t.co/FNnPy4yT9T', 'We first show that even though Bartik IV is estimated in the ""location"" space, its validity condition can be expressed in the ""industry"" space (i.e. the space of shocks g). \n\nFor shift-share IV validity, the covariance of g and relevant unobservables should be close to zero. https://t.co/UOxCdZ16A0', 'We then derive sufficient shock-level assumptions for this condition to hold. We think of shocks as being as-good-as-randomly assigned, with the impact of each shock shrinking as the sample grows\n\nWe also consider extensions with conditionally random shocks and panel variation https://t.co/KnSIVVUByQ', 'Lastly we caution that estimating aggregate shocks in the IV sample can make shift-share IV inconsistent, even when the shocks are random \n\nThis probably is analogous to the classic inconsistency of many-instrument 2SLS and can similarly be solved by split-sample shock estimation https://t.co/ZUFgWRh3cA', 'We hope this helps clarify how one may think of identification in shift-share IVs as ""coming from"" a natural shock experiment, and conclude with some practical advice for such settings\n\nOf course this is work in progress, so its helpfulness is up to you! Please send your thoughts']",18,06,1593