1 Department of Emergency Medicine and School of Epidemiology, Public Health and Preventive Medicine, University of Ottawa. jperry@ohri.ca.
2 Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada. jperry@ohri.ca.
3 Department of Neurosurgery and Department of Engineering Science & Mechanics, The Pennsylvania State University and Milton S. Hershey Medical Center, Hershey, PA.