1. Boston University School of Medicine, Department of Pediatrics, Boston, MA
2. Harbor-UCLA Medical Center, Department of Pediatrics, Los Angeles, CA
3. University of Maryland School of Medicine, Department of Pediatrics, Baltimore, MD
4. University of Arkansas for Medical Sciences, Department of Pediatrics, Little Rock, AR
5. Hennepin County Medical Center, Department of Pediatrics, Minneapolis, MN
6. Mary's Center for Maternal and Child Care, Washington, DC
7. Boston University School of Public Health, Data Coordinating Center, Boston, MA
8. Boston University School of Public Health, Department of Biostatistics, Boston, MA
9. U.S. Department of Agriculture Economic Research Service, Washington, DC