1. Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA
2. Department of Community Health, Brown University, Providence, Rhode Island, USA
3. Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA
4. Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA
5. Cardiovascular Epidemiology Research Unit, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA