1. Department of Biostatistics; West Virginia University; Morgantown WV U.S.A.
2. Department of Biostatistics; University of North Carolina at Chapel Hill; Chapel Hill NC U.S.A.
3. Carolina Population Center; University of North Carolina at Chapel Hill; Chapel Hill NC U.S.A.
4. Department of Health Behavior; University of North Carolina at Chapel Hill; Chapel Hill NC U.S.A.
5. Department of Medicine; University of North Carolina at Chapel Hill; Chapel Hill NC U.S.A.