[1] Sir Mortimer B Davis Jewish Hosp, Ctr Clin Epidemiol & Community Studies, Montreal, PQ H3T 1E2, Canada
[2] McGill Univ, Dept Epidemiol & Biostat, Montreal, PQ, Canada
[3] Univ Toronto, Hosp Sick Children, Toronto, ON M5G 1X8, Canada
[4] Univ London London Sch Hyg & Trop Med, Hlth Serv Res Unit, London WC1E 7HT, England
[5] Univ Liege, Dept Pharmacol, Liege, Belgium
[6] St Justine Hosp, Res Ctr, Montreal, PQ, Canada
[7] Univ Montreal, Fac Pharm, Montreal, PQ H3C 3J7, Canada