[1] Royal Victoria Hosp, Div Clin Epidemiol, Montreal, PQ H3A 1A1, Canada
[2] Beth Israel Deaconess Med Ctr, Div Gastroenterol, Boston, MA 02215 USA
[3] Massachusetts Gen Hosp, Dept Med, Boston, MA 02114 USA
[4] Childrens Hosp, Div Gastroenterol, Nutr Unit, Boston, MA 02115 USA
[5] McGill Univ, Ctr Hlth, Dept Med, Montreal, PQ, Canada
[6] McGill Univ, Jewish Gen Hosp, Montreal, PQ H3T 1E2, Canada