1. University of Bristol, Bristol Royal Infirmary; Rheumatology Unit; The Courtyard Marlborough Street Bristol UK BS2 8 HW
2. University Medical Center Utrecht; Rheumatology & Clinical Immunology; Box 85 500 3508 GA Utrecht Netherlands 3508 GA
3. Free University Hosptial; Department of Clinical Epidemiology; VE-9 oost PO Box 7057 1007 MB Amsterdam Netherlands
4. University of Ottawa; Institute of Population Health; 1 Stewart St. Room 312 Ottawa Ontario Canada K1N 6N5