1Institution of Public Health and Clinical Medicine/Rheumatology, University Hospital, Umeå, 901 85, Sweden
2Department of Rheumatology, Sunderby Hospital, Luleå, 971 80, Sweden
3Department of Rheumatology, Sundsvall Hospital, Sundsvall, 851 86, Sweden
4Department of Rheumatology, Östersund Hospital, Kyrkgatan, Östersund, 831 83, Sweden
5Institution of Statistics, Umeå University, Umeå, 90187, Sweden