1. Department of Social and Preventive Medicine/Groupe de Recherche Interdisciplinaire en Santé; Bureau 3108-1Pavillon 1420 Mont-Royal, University of Montreal, C.P. 6128 succursale Centre-Ville, Montréal (Québec), Canada H3C 3J7; phone: (514) 343-6111 (4957);
2. Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, and Institut National de Santé Publique du Québec, Canada
3. Department of Epidemiology, Biostatistics and Occupational Health, McGill University, and the Lea-Roback Research Center on Social Inequalities of Health, Montreal, Canada
4. Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Canada