1. Department of Pediatrics; University of North Carolina at Chapel Hill, School of Medicine; Chapel Hill North Carolina USA
2. Department of Sociology; University of North Carolina at Chapel Hill; Chapel Hill North Carolina USA
3. Department of Pediatrics; Medical University of South Carolina; Charleston South Carolina USA
4. Department of Medicine; Medical University of South Carolina; Charleston South Carolina USA
5. Cecil G Sheps Center for Health Services Research; University of North Carolina at Chapel Hill, School of Medicine; Chapel Hill North Carolina USA