Author Contributions: Dr Gray had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Gray, Javik.
Acquisition of data: Gray, Onwudiwe.
Analysis and interpretation of data: Gray, Hollingworth, Onwudiwe, Deyo, Jarvik.
Drafting of the manuscript: Gray, Hollingworth.
Critical revision of the manuscript for important intellectual content: Gray, Hollingworth, Onwudiwe, Deyo, Jarvik.
Obtained funding: Deyo.
Administrative, technical, or material support: Onwudiwe, Deyo, Jarvik.
Study supervision: Gray.
Financial Disclosures: None reported.
Funding/Support: This work was partially supported by grants P60 AR48093 and 5R01AR049373-04 from the National Institute for Arthritis, Musculoskeletal, and Skin Diseases.
Role of the Sponsors: The sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.
Disclaimer: The views expressed herein are not necessarily those of Agency for Healthcare Research and Quality (AHRQ), the Centers for Medicare & Medicaid Services, the National Institutes of Health, or the Department of Health and Human Services.
Additional Information: Drs Gray and Onwudiwe worked on this project while employed by the AHRQ. Dr Hollingworth worked on this project while employed by the University of Washington.
Additional Contributions: Leo Porter, AA, formerly of the Centers for Medicare & Medicaid Services (CMS) provided the Part B Extract Summary System data on which this study was based; Pamela Pope, BA, of CMS provided Part B fee-for-service enrollee data; and William Munier, MD, MBA, Artyom Sedrakyan, MD, PhD, and Chunliu Zhan, MD, PhD, of AHRQ provided comments on prior drafts of this paper. None of these persons received compensation for their contributions.