1. Division of Emergency Medicine; Children's Hospital of Pittsburgh; Department of Pediatrics; University of Pittsburgh School of Medicine; Pittsburgh; PA
2. Department of Emergency Medicine; University of Pennsylvania Perelman School of Medicine; Philadelphia; PA
3. Department of Biostatistics and Epidemiology; Center for Clinical Epidemiology and Biostatistics; University of Pennsylvania Perelman School of Medicine; Philadelphia; PA
4. Department of Pediatrics; Division of Emergency Medicine; A.I. duPont Hospital for Children; Wilmington; DE
5. Division of Emergency Medicine; The Children's Hospital of Philadelphia; Department of Pediatrics; University of Pennsylvania Perelman School of Medicine; Philadelphia; PA