[1] McGill Univ, Jewish Gen Hosp, Ctr Clin Epidemiol & Commun Studies, Montreal, PQ H3T 1E2, Canada
[2] London Sch Hyg & Trop Med, Hlth Serv Res Unit, London WC1, England
[3] Hop Notre Dame de Bon Secours, Montreal, PQ H2L 4K8, Canada
[4] Hop Pierre Boucher, Longueuil, PQ, Canada
[5] Hop Maison Neuve Rosemont, Montreal, PQ H1T 2M4, Canada
[6] McGill Univ, Ctr Hlth, Montreal, PQ, Canada
[7] Univ Laval, Quebec City, PQ G1K 7P4, Canada