1. Department of Medicine, Massachusetts General Hospital, Boston2National Bureau of Economic Research, Cambridge, Massachusetts3Department of Health Care Policy, Harvard Medical School, Boston, Massachusetts
2. Department of Health Care Policy, Harvard Medical School, Boston, Massachusetts
3. National Bureau of Economic Research, Cambridge, Massachusetts4Leonard D. Schaeffer Center for Health Policy and Economics, University of Southern California, Los Angeles
4. National Bureau of Economic Research, Cambridge, Massachusetts5Division of Health Policy and Management, School of Public Health, University of Minnesota, Minneapolis