Psychometric properties of morning joint stiffness duration and severity measures in patients with moderately to severely active rheumatoid arthritis

To assess the measurement properties of two single-item patient-reported outcome (PRO) measures that assessed the length of time (in minutes) and severity of morning joint stiffness (MJS) experienced each day. Data from two Phase 3, randomized placebo-controlled (and active-controlled [RA-BEAM]), clinical studies assessing the safety and efficacy of baricitinib in adults with moderately to severely active rheumatoid arthritis (RA) were used to evaluate the psychometric properties of the Duration of MJS and Severity of MJS PROs. Test-retest reliability of Duration of MJS and Severity of MJS was supported through large intraclass correlation coefficients among stable patients (coefficient range for both studies: 0.88 to 0.93). In support of construct validity, moderate correlations were evidenced between Duration of MJS and other related patient- and clinician-reported assessments of RA symptoms and patient functioning, whereas moderate-to-strong correlations were evidenced between these same patient- and clinician-reported assessments and Severity of MJS. Statistically significant differences between the median and mean values of Duration of MJS and Severity of MJS for differing categories of RA disease severity supported known-groups validity. Finally, large and statistically significant differences in change scores from Day 1 to Week 12 for patients defined as responders versus non-responders using the American College of Rheumatology 20 criteria supported the responsiveness of both PROs. Duration of MJS and Severity of MJS PROs demonstrated reliability, validity, and responsiveness in adults with moderately to severely active RA, supporting the measurement of these key symptoms in clinical trials.