PSYCHOMETRIC ASSESSMENT OF THE SWEDISH VERSION OF THE WORK ABILITY INDEX IN PATIENTS WITH CHRONIC PAIN IN SPECIALIZED CARE

OBJECTIVE: To evaluate the construct validity and internal consistency of the Work Ability Index (WAI) in patients with chronic pain in secondary and tertiary care. METHODS: Cross-sectional study based on 200 patients with chronic pain (> 3 months), with a final sample of 118 participants, 18–64-years-old. Construct validity was assessed by exploratory factor analysis for the structural validity of the WAI, and by correlating the WAI with EuroQol EQ-5D, Brief Pain Inventory pain severity and interference, Patient Health Questionnaire and Generalized Anxiety Disorder scales. The study also assessed the discriminant validity of the WAI for occupational status, and the validity of the single-item work ability score. Reliability was assessed by internal consistency. RESULTS: A single-factor model of WAI was supported. Internal consistency was good. Moderate correlations were found, except for Brief Pain Inventory pain severity, where the correlation was weak; hence, both convergent and divergent validity of the WAI were supported. The work ability score correlated strongly with the total WAI, and the discriminant validity for both was good. CONCLUSION: In patients with chronic pain in specialized care, the WAI and the work ability score displayed acceptable construct validity and internal consistency, supporting their use in a clinical context and research. LAY ABSTRACT Chronic pain may result in sick leave and work limitations. Assessment of work ability can be important for screening of needs and follow-up over time. Therefore, work ability among individuals with chronic pain should be assessed using valid measures. This study evaluated the measurement properties of the Work Ability Index among patients with chronic pain referred to a pain clinic. Analyses were performed to evaluate the degree to which the Work Ability Index measures work ability in a valid way, including aspects of construct validity and the interrelatedness among the items. The results of this study demonstrate acceptable measurement properties of the Work Ability Index among patients with chronic pain in specialized care; hence, the Work Ability Index could be used in pain care and research. In addition, the single-item work ability score included in the Work Ability Index was highly correlated with the total score and could be used as an alternative.