1. Department of Population Medicine, Harvard Medical School and Harvard Pilgrim Health Care Institute , Boston, MA 02215 , United States
2. Center for Research on Health Care, Division of General Internal Medicine, University of Pittsburgh, University of Pittsburgh Medical Center Present address: , Pittsburgh, PA 15213 , United States
3. Harvard Pilgrim Health Care Institute , Boston, MA 02215 , United States
4. Massachusetts General Hospital, Harvard Medical School , Boston, MA 02114 , United States
5. Department of Orthopedic Surgery, Emory University School of Medicine Present address: , Atlanta, GA 30329 , United States
6. Department of Medicine, Duke University , Durham, NC 27710 , United States
7. Duke-Margolis Center for Health Policy, Duke University , Durham, NC 27708 , United States