1. Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, United States Department of Health and Human Services, 8404 Irvington Avenue, Bethesda, MD 20892, USA
2. Institute for Fiscal Studies, London WC1E 7AE, UK
3. United Nations Children’s Fund, New York, NY 10017, USA
4. Environmental Influences on Child Health Outcomes, National Institutes of Health, Bethesda, MD 20852, USA
5. Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI 48109, USA
6. Department of Epidemiology and Biostatistics, Michigan State University, East Lansing, MI 48824, USA