1. Erasmus Medical Center; Department of General Practice; PO Box 2040 Rotterdam Netherlands 3000 CA
2. Erasmus Medical Center; Department of Public Health; PO Box 2040 Rotterdam Netherlands 3000 CA
3. Keele University; Arthritis Research UK Primary Care Centre; Keele Staffordshire UK ST5 5BG
4. VU University Medical Center; Department of Epidemiology and Biostatistics, EMGO Institute for Health and Care Research; PO Box 7057 Amsterdam Netherlands 1007 MB