1. From the Ottawa Health Research Institute (G.N., E.H., G.A.W.) and Department of Epidemiology and Community Medicine (G.N., G.A.W.), University of Ottawa, Ottawa, Canada; Department of Emergency Medicine (T.V., L.C.), University of Arizona, Tucson; and Division of Epidemiology and Biostatistics (D.R.), College of Public Health, University of Arizona, Tucson.