1. Center for Child Health Care Studies, Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care and Harvard Medical School, Boston, Massachusetts
2. Division of General Pediatrics, Children’s Hospital Boston, Boston, Massachusetts
3. Center for Health Studies, Group Health Cooperative, and Child Health Institute, Department of Pediatrics, University of Washington, Seattle, Washington
4. Division of Research, Kaiser Permanente, Oakland, California
5. Department of Pediatrics, Kaiser Permanente, Vallejo, California