[1] Ctr Addict & Mental Hlth, Social & Epidemiol Res Dept, London, ON N6G 4X8, Canada
[2] Univ Western Ontario, Dept Epidemiol & Biostat, London, ON N6A 5C1, Canada
[3] Univ Toronto, Dalla Lana Sch Publ Hlth, Toronto, ON M5T 3M7, Canada
[4] Univ Houston, Dept Psychol, Houston, TX 77204 USA
[5] Univ Western Ontario, Dept Psychol, Social Sci Ctr, London, ON N6A 5C2, Canada
[6] Curtin Univ Technol, Natl Drug Res Inst, Perth, WA 6845, Australia