[1] Harvard Med Sch, Brigham & Womens Hosp, Dept Med, Div Pharmacoepidemiol & Pharmacoecon, Boston, MA 02115 USA
[2] McGill Univ, Dept Epidemiol, Montreal, PQ, Canada
[3] McGill Univ, Dept Biostat, Montreal, PQ, Canada
[4] McGill Univ, Dept Occupat Hlth, Montreal, PQ, Canada