Author Contributions: Dr Nyweide 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: Nyweide, Weeks, Gottlieb, Fisher.
Acquisition of data: Weeks, Gottlieb, Fisher.
Analysis and interpretation of data: Nyweide, Weeks, Gottlieb, Casalino, Fisher.
Drafting of the manuscript: Nyweide.
Critical revision of the manuscript for important intellectual content: Nyweide, Weeks, Gottlieb, Casalino, Fisher.
Statistical analysis: Nyweide, Gottlieb.
Administrative, technical, or material support: Weeks, Fisher.
Study supervision: Weeks, Casalino, Fisher.
Financial Disclosures: Dr Casalino reports being a member of the board of directors of the American Medical Group Foundation, for which he is not compensated. The other authors report no disclosures.
Funding/Support: This research was funded by grant 20070129 from The Commonwealth Fund and grant PO1 AG19783 from the National Institute on Aging; access to data were provided by the Healthcare Organization Services database from IMS Health; Dr Nyweide reports completion of this research with support from the National Institute on Aging prior to becoming an employee at the Centers for Medicare & Medicaid Services, and he reports receiving reimbursement from IMS Health for expenses associated with a research meeting in August 2008.
Role of the Sponsor: The Commonwealth Fund, the National Institute on Aging, and IMS Health were not involved in the design of the study; analysis or interpretation of the data; or preparation, review, or approval of the manuscript.
Additional Contributions: We thank Jason Sutherland, PhD, The Dartmouth Institute for Health Policy and Clinical Practice, for his feedback on the analytical methods in the study; and Karen Swenson, MA, Kathy Ratcliffe, MS, Lorraine Bauman, MA, Ellen Westbrook, PhD, and Tom DiGiacinto, MBA, Marketing Initiatives International, a subsidiary of IMS Health, Bedford, New Hampshire, for their help with accessing the Healthcare Organization Services data and readily answering questions throughout this study. None of these individuals received compensation in association with their contributions to this article.