1. Division of Neonatology, Department of Pediatrics, and
2. Center for Outcomes Research, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania;
3. Leonard Davis Institute of Health Economics, University of Pennsylvania, Philadelphia, Pennsylvania;
4. Systems Research Initiative and Perinatal Research Unit, Kaiser Permanente Division of Research, Oakland, California; and
5. Department of Inpatient Pediatrics, Kaiser Permanente Medical Centers, Walnut Creek and Antioch, California