1. Department of Population Health Sciences, Duke University, Durham, North Carolina, USA.
2. Department of Epidemiology, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
3. Carolina Population Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
4. Department of Biostatistics, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
5. Center for AIDS Research, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
6. Department of Public Health and Community Medicine, Tufts University School of Medicine, Boston, Massachusetts, USA.