1. Department of Emergency Medicine; University of British Columbia; Vancouver British Columbia V5Z 1M9
2. Quality & Patient Safety; Vancouver Coastal Health; Vancouver British Columbia V5Z 1M9
3. Department of Statistics; University of British Columbia; Vancouver British Columbia V6T 1Z4
4. Centre for Clinical Epidemiology and Evaluation; Vancouver Coastal Health Research Institute; Vancouver British Columbia V5Z 1M9 Canada