[1] Queens Univ, Dept Med, Kingston Gen Hosp, Kingston, ON K7L 3N6, Canada
[2] Univ Toronto, Sunnybrook Hlth Sci Ctr, Sunnybrook Res Inst, Toronto, ON, Canada
[3] Univ Toronto, Interdept Div Crit Care Med, Toronto, ON, Canada
[4] Providence Hlth Care, Ctr Hlth Evaluat & Outcome Sci, Vancouver, BC, Canada
[5] Providence Hlth Care, Dept Med, Vancouver, BC, Canada
[6] Univ British Columbia, Vancouver, BC V5Z 1M9, Canada
[7] Univ British Columbia, Fraser Hlth Author, Dept Crit Care Med, Vancouver, BC V5Z 1M9, Canada
[8] Univ British Columbia, Dept Med, Vancouver, BC V5Z 1M9, Canada
[9] Vancouver Isl Hlth Author, Victoria, BC, Canada
[10] McGill Univ, Jewish Gen Hosp, Montreal, PQ H3T 1E2, Canada
[11] Harvard Univ, Sch Med, Dept Populat Med, Boston, MA USA
[12] Harvard Univ, Sch Med, Boston, MA USA
[13] Harvard Pilgrim Hlth Care Inst, Boston, MA USA
[14] Brigham & Womens Hosp, Boston, MA 02115 USA