Mohsen Sadatsafavi1, Don D Sin2. 1. Division of Respiratory Medicine, University of British Columbia, Vancouver, BC, Canada; Center for Clinical Epidemiology and Evaluation, Vancouver, BC, Canada. Electronic address: don.sin@hli.ubc.ca. 2. Division of Respiratory Medicine, University of British Columbia, Vancouver, BC, Canada; James Hogg Research Centre, St. Paul's Hospital, Vancouver, BC, Canada.