1. Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Rockville, Maryland, USA
2. Department of Epidemiology and Biostatistics, University of Texas Rural School of Public Health, College Station, Texas, USA
3. Department of Obstetrics and Gynecology, College of Medicine, The Ohio State University, Columbus, Ohio, USA
4. The EMMES Corporation, Rockville, Maryland, USA
5. Rollins School of Public Health, Emory University, Atlanta, Georgia, USA