[1] Johns Hopkins Univ, Dept Med, Div Clin Pharmacol, Baltimore, MD 21218 USA
[2] Johns Hopkins Univ, Sch Med, Baltimore, MD USA
[3] Johns Hopkins Univ, Berman Inst Bioeth, Baltimore, MD USA
[4] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Hlth Policy & Management, Baltimore, MD USA
[5] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Epidemiol, Baltimore, MD USA
[6] Childrens Hosp Philadelphia, Ctr Injury Res & Prevent, Dept Gen Pediat, Philadelphia, PA 19104 USA