[1] Harvard Med Sch, Dept Hlth Care Policy, Boston, MA 02115 USA
[2] Massachusetts Gen Hosp, Dept Med, Boston, MA 02114 USA
[3] NYU Grossman Sch Med, Dept Populat Hlth, New York, NY USA
[4] NYU Grossman Sch Med, Dept Med, New York, NY USA
[5] Univ Penn, Dept Med, Perelman Sch Med, Penn Med,Penn Primary Care, Philadelphia, PA USA
[6] Univ Penn, Leonard Davis Inst Hlth Econ, Philadelphia, PA 19104 USA