1. 1Department of Neurological Surgery and
2. 3Mayfield Clinic and Spine Institute, Cincinnati, Ohio
3. 2Center for Biostatistical Services, University of Cincinnati College of Medicine, and
4. 4Department of Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois; and
5. 5Department of Neurological Surgery, University of Virginia Health System, Charlottesville, Virginia