We thank Joseph Altonji, Steven Berry, Zachary Bleemer, Anne Case, Angus Deaton, Amy Finkelstein, Joshua Gottlieb, Jason Hockenberry, Anders Humlum, Dmitri Koustas, Neale Mahoney, Alex Mas, Costas Meghir, Fiona Scott Morton, Chima Ndumele, Seth Zimmerman, and many seminar participants for extremely valuable feedback. We benefited enormously from excellent research assistance provided by Felix Aidala, Krista Duncan, James Han, Mirko De Maria, Kelly Qiu, Shambhavi Tiwari, and Mai-Anh Tran. This project received financial support from Arnold Ventures and the National Institute on Aging (Grant P01-AG019783). We acknowledge the assistance of the Health Care Cost Institute (HCCI) and its data contributors, Aetna, Humana, and UnitedHealthcare, in providing the claims data analyzed in this study. HCCI had a right to review this research to guarantee we adhered to reporting requirements for the data related to patient confidentiality and the ban on identifying individual providers. Neither HCCI nor the data contributors could limit publication for reasons other than the violation of confidentiality requirements around patients and providers, nor could they require edits to the manuscript as a condition of publication. The opinions expressed in this article and any errors are those of the authors alone. This research was conducted while some of the authors were employees at the U.S. Department of the Treasury. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors and do not necessarily reflect the views or the official positions of the U.S. Department of the Treasury. Any taxpayer data used in this research was kept in a secured Treasury or IRS data repository, and all results have been reviewed to ensure that no confidential information has been disclosed. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.