1. Center for Injury Research and Prevention, and the Division of Emergency Medicine, The Children's Hospital of Philadelphia; Department of Pediatrics and Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
2. Department of Epidemiology, University of Washington, Seattle, Washington.
3. Department of Harborview Injury Prevention and Research Center, University of Washington, Seattle, Washington.
4. Department of Pediatrics, University of Washington, Seattle, Washington.
5. Department of Biostatistics, University of Washington, Seattle, Washington.
6. Department of Neurological Surgery, University of Washington, Seattle, Washington.
7. Department of Rehabilitation Medicine, University of Washington, Seattle, Washington.
8. Department of Anesthesiology, University of Washington, Seattle, Washington.