1. Schar School of Policy and Government, George Mason University , Arlington, VA 22201 , United States
2. National Bureau of Economic Research , Cambridge 02138, MA , United States
3. Institute of Labor Economics , 53113 Bonn , Germany
4. Division of Health Policy and Management, University of Minnesota School of Public Health , Minneapolis, MN 55455 , United States
5. RAND , Pittsburgh PA, 15213 , United States