1. Department of Health Research and Policy, Division of Epidemiology Stanford University Stanford California
2. Department of Health, Kinesiology, & Recreation University of Utah Salt Lake City Utah
3. Department of Physical Therapy & Athletic Training University of Utah Salt Lake City Utah
4. Department of Sports Medicine Norwegian School of Sport Sciences Oslo Norway
5. Department of Epidemiology and Biostatistics Memorial Sloan Kettering Cancer Center New York New York