1. Department of Emergency Medicine, University of Florida, 1329 SW 16th Street, Suite 5270, Gainesville, FL 32610, USA
2. Department of Biostatics, University of North Carolina, 135 Dauer Drive, Chapel Hill, N.C. 27599, USA
3. Department of Epidemiology, College of Medicine and College of Public Health and Health Professions, University of Florida, 2004 Mowry Road, Room 4218, P.O. Box 100231, Gainesville, FL 32610, USA