1. Harborview Injury Prevention and Research Center, University of Washington, Seattle, Washington, USA
2. Department of Pediatrics, University of Washington, Seattle, Washington, USA
3. Department of Epidemiology, University of Washington, Seattle, Washington, USA
4. Department of Neurological Surgery, University of Washington, Seattle, Washington, USA
5. Department of Rehabilitation Medicine, University of Washington, Seattle, Washington, USA
6. Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, Washington, USA