1. Department of Family and Preventive Medicine, University of California at San Diego, La Jolla, California
2. Section on Biostatistics, Wake Forest University School of Medicine, Winston-Salem, North Carolina and Medical Statistics Unit, London School of Hygiene and Tropical Medicine, London, England
3. Division of Geriatrics, University of California at Los Angeles Medical Center, Los Angeles, California
4. Department of Obstetrics and Gynecology, University of Texas Health Science Center, San Antonio, Texas
5. Department of Obstetrics and Gynecology, University of Iowa Hospital and Clinics, Iowa City, Iowa
6. Section on Biostatistics, Wake Forest University School of Medicine, Winston-Salem, North Carolina
7. National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland