[1] Univ British Columbia, Vancouver Coastal Hlth Res Inst, Ctr Clin Epidemiol & Evaluat, 7th Floor,828 W 10 Ave, Vancouver, BC V5Z 1M9, Canada
[2] Univ Alberta, Sch Publ Hlth, Ctr Hlth Promot Studies, Edmonton, AB T6G 2M7, Canada
[3] Vancouver Coastal Hlth Res Inst, Ctr Clin Epidemiol & Evaluat, Vancouver, BC, Canada
[4] Univ British Columbia, Sch Populat & Publ Hlth, Vancouver, BC V5Z 1M9, Canada
[5] Univ British Columbia, Fac Hlth & Social Dev, Vancouver, BC V5Z 1M9, Canada
[6] Univ Birmingham, Sch Social Policy, Hlth Serv Management Ctr, Birmingham B15 2TT, W Midlands, England