1. Department of Physical Medicine and Rehabilitation Østfold Hospital Trust Sarpsborg Norway
2. Department of Health and Welfare Østfold University College Fredrikstad Norway
3. Department of Public Health and Nursing Norwegian University of Science and Technology Trondheim Norway
4. Department of Clinical and Molecular Medicine Norwegian University of Science and Technology Trondheim Norway
5. Department of Surgery St. Olavs Hospital Trondheim University Hospital Trondheim Norway
6. Oslo Centre of Biostatistics and Epidemiology Oslo University Hospital Oslo Norway