1. Injury Prevention Research Center and Department of Epidemiology; University of North Carolina at Chapel Hill; Chapel Hill NC USA
2. Department of Health Behavior; University of North Carolina at Chapel Hill; Chapel Hill NC USA
3. Department of Epidemiology; University of North Carolina at Chapel Hill; Chapel Hill NC USA
4. Injury Prevention Research Center; University of North Carolina at Chapel Hill; Chapel Hill NC USA
5. Duke Clinical Research Institute; Durham NC USA