1. Group Health Research Institute, 1730 Minor Avenue, Suite 1600, Seattle, WA 98101, USA
2. Department of Epidemiology, University of Washington, Seattle, WA 98101, USA
3. Department of Biostatistics, University of Washington, Seattle, WA 98101, USA
4. Departments of Family Medicine and Health Services, University of Washington, Seattle, WA 98101, USA
5. Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109, USA