Reliability and Validity of the Work Instability Scale for Rheumatoid Arthritis

Abstract

ObjectiveThe objective was to evaluate the psychometric properties of the Rheumatoid Arthritis-Work Instability Scale (RA-WIS) in a clinical trial setting. MethodsSecondary analyses were conducted using data from a 56-week, randomized controlled trial of patients with early rheumatoid arthritis (RA). Patient-reported outcome measures included the RA-WIS, the Health Assessment Questionnaire (HAQ), the Rheumatoid Arthritis Quality of Life Questionnaire, and the Global Assessment of Disease Activity and Pain, data for which were collected at baseline and at weeks 12, 16, 24, and 56. Data were analyzed for reliability, validity, and responsiveness. ResultsAmong 148 patients whose data were analyzed, more than half were women (56.1%) with a mean age of 46.8 years. On average, patients experienced RA symptoms for 8.7 months; the mean 28-Joint Disease Activity Score (DAS28) was 5.9, and the mean HAQ – Disability Index was 1.3. The RA-WIS demonstrated excellent internal consistency and test-retest reliability (α = 0.89 and intraclass correlation coefficient = 0.91, respectively). At baseline and week 24, moderate to strong correlations were seen between RA-WIS total scores and the HAQ, the Global Assessment of Disease Activity, and the Pain Rheumatoid Arthritis Quality of Life Questionnaire, ranging from 0.47 to 0.81 (all P < 0.0001). Mean RA-WIS total scores and work disability risk levels discriminated between clinical severity scores on the DAS28, the HAQ – Disability Index, and the Physician Global Assessment of Disease Activity (all P < 0.05). Mean baseline to week 24 RA-WIS total change scores were significantly different among American College of Rheumatology responder groups (P ≤ 0.0001) and between DAS28 remission status groups (P < 0.001). ConclusionsThese findings provide evidence supporting the reliability, validity, and responsiveness of the RA-WIS for evaluating work disability in patients with RA in a clinical trial setting.