1. Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania.
2. Division of Epidemiology, School of Public Health, University of California, Berkeley, Berkeley, California.
3. Department of Obstetrics and Gynecology, University of Massachusetts Medical School, Worcester, Massachusetts.
4. Department of Quantitative Health Sciences, University of Massachusetts Medical School, Worcester, Massachusetts.
5. Division of Research, Kaiser Permanente, Oakland, California.
6. Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts.