1. Department of Epidemiology, University of North Carolina, Chapel Hill, North Carolina.
2. Department of Epidemiology, Emory University, Atlanta, Georgia.
3. Division of Epidemiology and Biostatistics, School of Public Health, University of California, Berkeley, California.
4. GlaxoSmithKline, Singapore, Singapore.
5. Department of Epidemiology, Columbia University, New York, New York.
6. Department of Medicine, Columbia University, New York, New York.