1. From the Division of General Pediatrics, Childrens Hospital, Los Angeles, California;
2. Center for Pediatric Health Outcomes Research, Department of Pediatrics, University of Southern California, Los Angeles, California;
3. Division of Biostatistics & Outcomes Assessment, Los Angeles County and University of Southern California Medical Center, Los Angeles, California;
4. Health Services Research and Development Service, Greater Los Angeles Veterans' Affairs Healthcare System, Los Angeles, California;
5. Southern California Evidence-Based Practice Center, RAND, Santa Monica, California;
6. Statistics Group, RAND, Santa Monica, California;
7. Division of Infectious Diseases, Childrens Hospital, Los Angeles, California;
8. Department of Pediatrics, Southern California Kaiser–Permanente Health Care Program, Panorama City, California.