1. Environmental Health Sciences Graduate Program, University of California, Irvine, Irvine, California, USA
2. Department of Public Health Sciences, University of California, Davis, Davis, California, USA
3. Program in Public Health, University of California, Irvine, Irvine, California, USA
4. Department of Epidemiology, and
5. Department of Obstetrics and Gynecology, Brown University, Providence, Rhode Island, USA
6. Department of Statistics, and
7. Department of Epidemiology, University of California, Irvine, Irvine, California, USA