1. University of South Carolina, Arnold School of Public Health, Department of Epidemiology and Biostatistics, Columbia, SC, USA
2. University of Mississippi Medical Center, Department of Preventive Medicine, Jackson, MS, USA
3. University of Missouri Columbia, School of Medicine, Biostatistics and Research Design Unit, Columbia, MO, USA
4. University of South Carolina, School of Medicine, Department of Family and Preventive Medicine, Columbia, SC, USA