1 Department of Family Practice (McGregor), University of British Columbia; Centre for Clinical Epidemiology & Evaluation (McGregor), Vancouver Coastal Health Research Institute, Vancouver, BC; University of California San Francisco (Harrington), San Francisco, Calif. mrgret@mail.ubc.ca.
2 Department of Family Practice (McGregor), University of British Columbia; Centre for Clinical Epidemiology & Evaluation (McGregor), Vancouver Coastal Health Research Institute, Vancouver, BC; University of California San Francisco (Harrington), San Francisco, Calif.