Psychometric properties of the single-item measure, severity of worst tiredness, in patients with moderately to severely active rheumatoid arthritis

BACKGROUND To assess the reliability, validity, and responsiveness to treatment change of the single-item measure, Severity of Worst Tiredness, in patients with rheumatoid arthritis (RA). METHODS Data from two Phase 3, randomized, placebo-controlled (RA-BUILD; and active-controlled [RA-BEAM]), clinical studies of the efficacy of baricitinib in adults with moderately to severely active RA were used. The psychometric properties of the single-item measure, Severity of Worst Tiredness, were assessed, including test-retest reliability, convergent and discriminant validity, known-groups validity, and responsiveness, using other patient- and clinician-reported outcomes frequently assessed in RA patients. RESULTS Test-retest reliability of the Severity of Worst Tiredness was supported through large intraclass correlation coefficients (0.89 ≤ ICC ≤ 0.91). Moderate-to-large correlations were observed between this patient-reported outcome (PRO) and other related patient- and clinician-reported assessments of RA symptoms and patient functioning, supporting construct validity of the measure (│r│ ≥ 0.41). The instrument also displayed known-groups validity through statistically significant differences between mean values of the Severity of Worst Tiredness defined using other indicators of RA severity. Finally, responsiveness was supported by large and statistically significant differences in change scores from Day 1 to Week 12 for patients comparing responders and nonresponders using the American College of Rheumatology 20 (ACR20) criteria. CONCLUSION The Severity of Worst Tiredness PRO demonstrated adequate reliability, validity, and responsiveness in clinical trials of adults with moderately to severely active RA and is fit for purpose in this patient population.