[1] Harvard Med Sch, Dept Hlth Care Policy, Boston, MA 02115 USA
[2] Massachusetts Gen Hosp, Dept Med, Boston, MA 02114 USA
[3] Natl Bur Econ Res, Cambridge, MA 02138 USA
[4] Columbia Univ, Dept Econ, New York, NY 10027 USA
[5] Weill Cornell Med Coll, Dept Heallhcare Policy & Res, New York, NY USA
[6] Weill Cornell Med Coll, Dept Med, New York, NY USA
[7] Stanford Univ, Dept Polit Sci, Stanford, CA 94305 USA
[8] NYU, Dept Polit, New York, NY USA