[1] Childrens Hosp Philadelphia, Div Emergency Med, Colket Translat Res Bldg, Philadelphia, PA 19104 USA
[2] Childrens Hosp Philadelphia, Ctr Injury Res & Prevent, Philadelphia, PA 19104 USA
[3] Univ Penn, Dept Biostat & Epidemiol, Philadelphia, PA 19104 USA
[4] Brown Univ, Alpert Med Sch, Dept Pediat, Dept Emergency Med, Providence, RI 02912 USA
[5] Hasbro Childrens Hosp, Providence, RI USA
[6] Univ Penn, Perelman Sch Med, Philadelphia, PA 19104 USA