1. Yale University, 165 Whitney Avenue, New Haven, CT 06520, and NBER (e-mail: )
2. Department of Economics, Dartmouth College, 6016 Rockefeller Hall, Hanover, NH 03755, and NBER (e-mail: )
3. Department of Emergency Medicine, Massachusetts General Hospital, Zero Emerson Place, Suite 3B, Boston, MA 02114, and Harvard University (e-mail: )
4. Massachusetts General Hospital and Harvard University (e-mail: )
5. Yale-New Haven Hospital, and Yale University (e-mail: )