1 Institute for Primary Care and Health Sciences, Keele University, Keele.
2 Rheumatology, Derby Teaching Hospitals NHS Foundation Trust, Derby.
3 University of Edinburgh, Edinburgh.
4 Research Institute for Primary Care and Health Sciences, Keele University, Keele, and Haywood Academic Rheumatology Centre, Staffordshire and Stoke-on-Trent Partnership Trust, Stoke-on-Trent.