Development of the Salford rheumatoid arthritis foot evaluation instrument: A sequential exploratory mixed methods design
Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease that commonly manifests in the feet as pain, swelling and deformity. These symptoms often have extensive and severe mutlidimensional consequences for people's lives and can be evaluated using a class of subjective outcome measures known as patient-reported outcome measures (PROMs). PROMs have been advocated by the Darzi report and are central to reforms in the NHS.\ud Therefore, the aim of this thesis was to develop a new and novel PROM, the Salford Rheumatoid Arthritis Foot Evaluation Instrument (SAFE), using a clinimetric approach and featuring an adequately pre-tested nomothetic (fixed scale) and idiographic (patient-specific scale) assessment\ud strategy. A mixed methods approach was employed to develop the SAFE, with the formulation and implementation of a four phase sequential exploratory fully mixed methods design (SEMMD) that featured equal priority between the qualitative and quantitative components.\ud The four phase SEMMD enabled the strategic and effective combination of methods to produce a PROM that is firmly rooted in the views and experiences of people with feet affected by RA. The nomothetic scale of the SAFE has evidence for face, content and convergent validity (Spearman-Rank co-efficients: 0.62 - 0.80) and excellent one week test-retest reliability (intra-class correlation coefficients: 0.86 - 1.00 ). The idiographic scale has evidence for face and content validity.\ud The SAFE is a tool for both clinical practice and clinical research. In order to realise the full potential of the SAFE, further research will be undertaken to refine, develop the PROM and integrate it into clinical practice. Initially, it will be necessary to demonstrate additional measurement properties for the nomothetic scale, including clinical interpretability and responsiveness and also\ud necessary to demonstrate quantitative measurement properties for the idiographic scale. Long term, the SAFE will be redeveloped using item response theory and implemented as a computerised adaptive test.