1. Faculty of Health and Sport, University of Agder
2. Division of Rheumatology, Department of Medicine, Sørlandet Hospital HF, Kristiansand
3. Oslo Centre of Biostatistics and Epidemiology, Research Support Services, Oslo
4. Department of Rheumatology, Martina Hansens Hospital, Bærum
5. Department of Neuroscience, Division of Rheumatology, Norwegian University of Science and Technology, Trondheim, Norway