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

OBJECTIVES: To evaluate the psychometric properties of an index based on 3 patient reported outcomes 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 analyzed 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. CONCLUSIONS: The study showed satisfactory psychometric properties of the PRO-CLARA