1. Department of Rheumatology, Östersund Hospital, Östersund and Institution of Clinical Sciences, Lund University Hospital, Lund, Sweden; 2Department of Rheumatology, Institution of Clinical Sciences, Lund University Hospital, Lund, Sweden; 3Department of Rheumatology, Umeå University Hospital, Umeå, Sweden; and 4Department of Statistics, Umeå University, Umeå, Sweden