1. Department of Epidemiology and Biostatistics, Drexel University School of Public Health, Philadelphia, Pennsylvania 19102;
2. Division of Research, Kaiser Permanente Medical Care Program, Oakland, California 94612
3. Department of Epidemiology, University of North Carolina, Chapel Hill, North Carolina 27599
4. School of Nursing, University of Pennsylvania, Philadelphia, Pennsylvania 19104
5. Environmental Health Investigations Branch, California Department of Health Services, Richmond, California 94804
6. Department of Pediatrics, 7Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
7. Colorado Department of Public Health and Environment, Denver, Colorado 80246
8. Department of Pediatrics, 10University of Colorado, Denver; Health Sciences Center, JFK Partners, Denver, Colorado 80218
9. National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia 30333