1. Department of Epidemiology, University of North Carolina at Chapel Hill, Chapel-Hill, North Carolina.
2. Collaborative Studies Coordinating Center, Department of Biostatistics, School of Public Health, University of North Carolina at Chapel Hill, Chapel-Hill, North Carolina.
3. Department of Epidemiology, University of Michigan, Ann Arbor, Michigan.
4. Department of Epidemiology and Preventive Medicine, University of Maryland at Baltimore, Baltimore, Maryland.
5. School of Nursing and School of Medicine, University of Mississippi Medical Center, Jackson, Mississippi.