1. Department of Pediatrics, University of Texas Southwestern Medical Center, Division of Critical Care Services, Children's Medical Center of Dallas, Dallas, Texas.
2. Safar Center for Resuscitation Research, Children's Hospital of Pittsburgh, University of Pittsburgh, Pittsburgh, Pennsylvania.
3. Department of Epidemiology, University of Pittsburgh, Pittsburgh, Pennsylvania.
4. Penn State Children's Hospital, Pennsylvania State University College of Medicine, Hershey, Pennsylvania.