1. Division of General Pediatrics, Department of Pediatrics, Mattel Children's Hospital, David Geffen School of Medicine at UCLA, Los Angeles, California 90024;
2. RAND, Santa Monica, California 90401
3. Division of Adolescent and Young Adult Medicine, Department of Medicine, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115
4. Department of Society, Human Development, and Health, Harvard School of Public Health, Boston, Massachusetts 02115
5. Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, 02115
6. Division of General Pediatrics, Department of Medicine, Children's Hospital Boston, Boston, Massachusetts 02115