1. Department of Pediatrics, Pontificia Universidad Católica de Chile, Santiago, Chile
2. School of Public Health, University of Alabama at Birmingham, Birmingham, Alabama
3. Health Economics Resource Center, Center for Health Care Evaluation, and Cooperative Studies Program, Veterans Affairs Palo Alto Health Care System, Palo Alto, California; Department of Health Research and Policy, Stanford University, Stanford, California
4. Department of Pediatrics and Cardiovascular Research Institute, University of California, San Francisco, California
5. Department of Pediatrics, University of Alabama at Birmingham, Birmingham, Alabama