1. DeltaQuest Foundation, Inc., Concord, MA 01742, USA
2. Departments of Medicine and Orthopaedic Surgery, Tufts University School of Medicine, Boston, MA 02111, USA
3. Department of Measurement, Evaluation, Statistics, & Assessment, Boston College Lynch School of Education and Human Development, Chestnut Hill, MA 02467, USA
4. Department of Epidemiology & Population Health, Albert Einstein College of Medicine, Bronx, NY 10461, USA
5. Division of Spine Surgery, Sunnybrook Health Sciences Centre, Toronto, ON M4N 3M5, Canada
6. Department of Surgery, University of Toronto, Toronto, ON M4N 3M5, Canada
7. Division of Orthopedic Surgery, Sunnybrook Health Sciences Centre, Toronto, ON M4N 3M5, Canada