[1] Univ British Columbia, St Pauls Hosp, Dept Med, Ctr Hlth Evaluat & Outcome Sci, Vancouver, BC V5Z 1M9, Canada
[2] DM STAT Inc, Medford, MA USA
[3] Boston Univ, Sch Med, Northampton, MA USA
[4] Boston Univ, Sch Publ Hlth, Northampton, MA USA
[5] Smith Coll, Dept Math, Northampton, MA 01063 USA
[6] Boston Univ, Dept Med, Gen Internal Med Sect, CARE Unit, Vancouver, WA USA
[7] Boston Univ, Dept Social & Behav Sci, Vancouver, WA USA