1. Division of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Palo Alto, California;
2. Statistics and Epidemiology Unit, RTI International, Research Triangle Park, North Carolina;
3. Department of Pediatrics, Rainbow Babies & Children's Hospital, Case Western Reserve University, Cleveland, Ohio;
4. Statistics and Epidemiology Unit, RTI International, Rockville, MD;
5. Department of Pediatrics, University of Iowa, Iowa City, Iowa;
6. Department of Pediatrics, Women and Infants' Hospital, Brown University, Providence, Rhode Island; and
7. Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland