1 Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts (M.P.C.).
2 University of British Columbia, St. Paul's Hospital, and the Centre for Health Evaluation and Outcome Sciences, Vancouver, British Columbia, Canada (R.S.).
3 Montreal Children's Hospital, McGill University, Montreal, Quebec, Canada (K.P.).
4 McGill University Health Centre, McGill University, Montreal, Quebec, Canada (C.Y.).
5 University of British Columbia and Vancouver General Hospital, Vancouver, British Columbia, Canada (D.S.).