Psychometric properties of an index of three patient-reported outcome (PRO) measures, termed the CLinical ARthritis Activity (PRO-CLARA) in patients with rheumatoid arthritis. The NEW INDICES study

Objective To evaluate the psychometric properties of an index based on 3 patient-reported outcome measures, termed PRO-CLinical ARthritis Activity (PRO-CLARA), in order to facilitate rapid and easy rheumatoid arthritis (RA) activity assessment in daily routine. Methods 196 patients partially or not responding to disease modifying anti-rheumatic drugs (DMARDs) consented to participate in a multicentre cross-sectional study. For the evaluation of the psychometric properties of the PRO-CLARA, this population has been compared to another cohort of 247 outpatients with RA who were participating in a long-term observational study and who satisfying minimal disease activity and remission definitions. All patients completed the PRO-CLARA, combining patient's physical function, self-administered tender joint count and perception of global health status into a single measure of disease activity. Additional comparator composite indices were analysed. Internal consistency was assessed with Cronbach's alpha coefficient. A confirmatory factor analysis was carried out to test factor structure. Concurrent validity was analysed using Spearman's correlations and cross-tabulations. Discriminant validity to distinguish patients with active and non-active disease was assessed with receiver operating characteristic (ROC) curve analysis. For agreement analysis, kappa statistics were calculated. Results In testing for internal consistency, we found that Cronbach's alpha for the PRO-CLARA was 0.893, indicating high reliability. PRO-CLARA proved to be significantly correlated to established RA activity assessment tools. The area under ROC curve of the PRO-CLARA gives identical results to those provided by other comparator indices. Conclusion The study showed satisfactory psychometric properties of the PRO-CLARA