[1] Univ Maryland Baltimore Cty, Sch Publ Policy, 1000 Hilhop Circle, Baltimore, MD 21250 USA
[2] Maryland Inst Emergency Med Serv Syst, 5111 Berwyn Rd, College Pk, MD 20740 USA
[3] Univ Maryland, Sch Med, Dept Epidemiol & Publ Hlth, 660 Redwood St, Baltimore, MD 21201 USA