1. HealthPartners Institute for Education and Research, HealthPartners, Minneapolis, Minnesota;
2. Department of Pediatrics, and
3. Institute for Health Research, Kaiser Permanente Colorado, Denver, Colorado;
4. Division of Epidemiology and Community Health, University of Minnesota, Minneapolis, Minnesota;
5. Department of Pediatrics, Kaiser Permanente San Francisco, San Francisco, California; and
6. Division of Research, Kaiser Permanente Northern California, Oakland, California