1. Department of Pediatrics, School of Medicine, Harborview Injury Prevention and Research Center University of Washington 325 Ninth Avenue, PO Box 359960 Seattle WA 98104 USA
2. Department of Epidemiology, School of Public Health University of Washington Box 351619 Seattle WA 98195 USA
3. College of Education University of Washington Box 353600 Seattle WA 98195 USA