1. Clinical Epidemiology Unit, Massachusetts General Hospital, Boston, MA
2. Department of Medicine, University of California San Francisco, San Francisco, CA
3. Division of Research, Kaiser Permanente of Northern California, Oakland, CA
4. Department of Research and Evaluation, Kaiser Permanente of Southern California, Pasadena, CA
5. Department of Epidemiology, University of California San Francisco, San Francisco, CA
6. Department of Biostatistics, University of California San Francisco, San Francisco, CA
7. Department of Health Research and Policy, Stanford University School of Medicine, Palo Alto, CA