1. The Parker Institute, Department of Rheumatology, Copenhagen University Hospital Bispebjerg and Frederiksberg Hospital, Nordre Fasanvej 57, 2000 Frederiksberg, Denmark
2. Institute of Public Health, University of Southern Denmark, 5000 Odense, Denmark
3. Section for Statistics and Data Analysis, Department of Applied Mathematics and Computer Science, Technical University of Denmark, 2800 Lyngby, Denmark
4. Oregon Health & Science University, Portland, OR 97239, USA