1. Department of Environmental Health, Emory University Rollins School of Public Health, Atlanta, GA 30322, USA
2. Department of Epidemiology, Emory University Rollins School of Public Health, Atlanta, GA 30322, USA
3. National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, Atlanta, GA 30345, USA
4. Department of Epidemiology, University of Alabama at Birmingham School of Public Health, Birmingham, AL 35294, USA