1. Division of Neurosurgery, Department of Surgery, Duke University Medical Center, Durham, North Carolina.
2. Center for Neurosurgical Outcomes Research, Maxine Dunitz Neurosurgical Institute, Department of Neurosurgery, Cedars-Sinai Medical Center, Los Angeles, California.
3. Department of Neurosurgery, University of Louisville and Robley Rex VA, Louisville, Kentucky.