1. Division of Biostatistics & Epidemiology, School of Public Health & Health Sciences, University of Massachusetts, Amherst, Massachusetts.
2. Current address: Menzies Research Institute, University of Tasmania, Hobart, Australia.
3. Kaiser Permanente, Oakland, California.
4. Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
5. Department of Kinesiology, School of Public Health & Health Sciences, University of Massachusetts, Amherst, Massachusetts.
6. Baystate Medical Center, Springfield, Massachusetts.