1. Carolina Population Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
2. Department of Sociology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
3. Department of Maternal and Child Health, Gillings School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
4. Department of Epidemiology and Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
5. Epidemiology Research Team, Department of Radiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA