This study was supported by the Agency for Health Research and Quality’s Comparative Health System Performance Initiative under grant number 1U 19HS024075, which investigates how health care delivery systems promote health practices. evidence-based and patient-centred outcomes research in the delivery of care. The research was also partially funded by a research grant from AMGA to the Center for Health Care Organization and Innovation Research. The content is the sole responsibility of the authors and does not necessarily represent the views of AMGA. The statements, findings, conclusions, views and opinions contained and expressed in this article are based in part on data obtained under license from IQVIA Information Services (OneKey Subscription Information Services 2010–18, IQVIA Inc ., All rights reserved). The statements, findings, conclusions, views and opinions contained and expressed herein are not necessarily those of IQVIA Inc. or any of its affiliates or subsidiaries. The American Medical Association (AMA) was the source of the raw physician data; statistics, tables and tabulations were prepared by the authors using data from the AMA Physician Masterfile. The authors appreciate critical comments from expert panelists. The authors also thank Timothy T. Brown for his helpful consultation for the econometric analyses.