1. Sunnybrook Research Institute, Sunnybrook Health Sciences Center, Toronto, Ontario, Canada.
2. Clinical Epidemiology Program, Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada.
3. Division of Neurosurgery, University of Ottawa, Ottawa, Ontario, Canada.
4. Department of Critical Care, Sunnybrook Health Sciences Center, Toronto, Ontario, Canada.
5. Interdepartmental Division of Critical Care, University of Toronto, Toronto, Ontario, Canada.
6. Division of Neurosurgery, Sunnybrook Health Sciences Center, University of Toronto, Toronto, Ontario, Canada.
7. Department of Research Design and Biostatistics, Sunnybrook Health Sciences Center, Toronto, Ontario, Canada.
8. Department of Surgery, Sunnybrook Health Sciences Center, University of Toronto, Toronto, Ontario, Canada.
9. Keenan Research Center of the Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, Ontario, Canada.
10. Department of Medicine, St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada.