1. Departments of Medicine and Epidemiology and Biostatistics, University of California San Francisco , San Francisco, CA, USA
2. VA Division of General Internal Medicine, University of California San Francisco , San Francisco, CA, USA
3. Kaiser Permanente Washington Health Research Institute, Kaiser Permanente Washington , Seattle, WA, USA
4. Departments of Surgery and Radiology, University of Vermont , Burlington, VT, USA
5. The Dartmouth Institute for Health Policy and Clinical Practice and Dartmouth Cancer Center, Dartmouth Geisel School of Medicine , Lebanon, NH, USA
6. Department of Public Health Sciences, University of California, Davis , Davis, CA, USA