1. From McMaster University and St. Joseph's Hospital, Hamilton, Ontario, Canada; Community Medicine, University of Ottawa, Ontario, Canada; Harvard Vanguard Medical Associates, Brigham and Women's Hospital, Boston, Massachusetts; Royal Infirmary, Glasgow, United Kingdom; Addenbrooke's Hospital, Cambridge, United Kingdom; and Centro di Riferimento Regionale per la Trombosi, Azienda Ospedaliero-Universitaria Careggi, Florence, Italy.