1. Department of Health Sciences Research Division of Epidemiology, Mayo Clinic, Rochester, Minnesota.
2. Department of Physical Medicine and Rehabilitation, Mayo Clinic, Rochester, Minnesota.
3. Long Health Economics Consulting, St. Paul, Minnesota.
4. Department of Health Sciences Research, Division of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, Minnesota.
5. Department of Surgery, University of Vermont Medical College, Burlington, Vermont.
6. Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine and Rehabilitation Hospital of Indiana, Indianapolis, Indiana.