1. From the School of Population and Public Health (J.D.E.), the Department of Physical Therapy (S.K.M., L.A.B.), the Department of Neurology (P.A.T.), and the Graduate Program in Rehabilitation Science (M.A.L.), University of British Columbia, British Columbia, Canada; and the Department of Community Health and Epidemiology (A.R.L.), Dalhousie University, Halifax, Nova Scotia, Canada.