[1] Univ Manitoba, Max Rady Coll Med, Rady Fac Hlth Sci, Dept Internal Med, Winnipeg, MB, Canada
[2] Washington Univ, Dept Biostat, St Louis, MO 63110 USA
[3] St Josephs Hosp, Dign Hlth, Phoenix, AZ USA
[4] Univ Alabama Birmingham, Dept Biostat, Birmingham, AL 35294 USA
[5] Cleveland Clin, Neurol Inst, Mellen Ctr Multiple Sclerosis, Cleveland, OH 44106 USA
[6] Univ Manitoba, Max Rady Coll Med, Rady Fac Hlth Sci, Dept Community Hlth Sci, Winnipeg, MB, Canada