[1] Univ Penn, Robert Wood Johnson Clin Scholars Program, Philadelphia, PA 19104 USA
[2] Univ Penn, Leonard Davis Inst Hlth Econ, Philadelphia, PA 19104 USA
[3] Harvard Univ, Sch Med, Childrens Hosp, Dept Med, Boston, MA 02115 USA
[4] Harvard Univ, Sch Med, Brigham & Womens Hosp, Dept Med, Boston, MA 02115 USA
[5] Childrens Hosp Philadelphia, Dept Gen Pediat, Philadelphia, PA 19104 USA
[6] Univ Calif San Diego, Sch Med, Childrens Hosp & Hlth Ctr, San Diego, CA 92103 USA
[7] George Washington Univ, Sch Med, Childrens Natl Med Ctr, Washington, DC USA