Published on in Vol 13, No 1 (2011): Jan-Mar
1 Group Health Research Institute, Seattle, WA, United States
2 Group Health Permanente, Seattle, WA, United States
3 Medical School, University of Washington, Seattle, WA, United States
4 School of Public Health, University of Washington, Seattle, WA, United States
5 Department of Biostatistics, University of Washington, Seattle, WA, United States
*all authors contributed equally