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