1. Brigham and Women's Hospital Harvard Medical School Boston MA USA
2. Diakonhjemmet Hospital Department of Rheumatology Oslo Norway
3. Institute of Clinical Medicine University of Oslo Oslo Norway
4. University of Arizona Arthritis Center University of Arizona College of Medicine Tucson AZ USA
5. Department of Epidemiology and Biostatistics Mel and Enid Zuckerman College of Public Health University of Arizona Tucson AZ USA