1. Duke Clinical Research Institute, and
2. Department of Pediatrics, Duke University Medical Center, Durham, North Carolina;
3. Division of Neonatal–Perinatal Medicine, School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina;
4. Pediatrix-Obstetrix Center for Research and Education, Sunrise, Florida; and
5. John E. Walker Department of Economics, Clemson University, Clemson, South Carolina