[1] McGill Univ, Montreal, PQ, Canada
[2] Royal Victoria Hosp, Div Clin Epidemiol, Montreal, PQ H3A 1A1, Canada
[3] Royal Victoria Hosp, Resp Epi & Clin Res Unit, Montreal, PQ H3A 1A1, Canada
[4] McGill Univ, Sch Phys & Occupat Therapy, Montreal, PQ, Canada
[5] McGill Univ, Fac Med, Montreal, PQ, Canada