Scale development of the Osteoarthritis Conceptualisation Questionnaire: Phase 3 convergent validity and test-retest...

The Osteoarthritis Conceptualisation Questionnaire (OACQ) aims to evaluate people's understanding of osteoarthritis. This study aimed to evaluate construct validity and reliability among those with painful knee osteoarthritis. Using previously collected data (n = 454, n = 336 female; 64 ± 9yrs) and a second confirmatory sample (n = 64, n = 47 female; 67 ± 8yrs), the scale properties of the four-dimensional (i.e., subscale) OACQ were evaluated. Both samples were compared to a Rasch model indicative of measurement to evaluate the targeting, category ordering, unidimensionality, local dependence, person fit, internal consistency, and differential item functioning (DIF). Convergent validity was evaluated in both samples, evaluating associations between the OACQ and related assessments. Test-retest reliability was evaluated in the second sample over a one-week period. Results showed that targeting was generally adequate, although all OACQ subscales showed unidimensionality. Two subscales demonstrated person misfit; however, sensitivity analyses revealed the misfit had minimal impact on scale functioning. Internal consistency was good for all subscales, and DIF was consistent with expectations. Rasch findings were supported in the confirmatory sample. The OACQ had correlations with related measures supportive of convergent validity and demonstrated good to excellent reliability (ICC = 0.89, 95% CI [0.80 to 0.94]). This study provides evidence supportive of validity and reliability of the OACQ as an assessment of how people understand knee osteoarthritis. It has utility as a tool for clinicians and researchers to understand how their patients/participants conceptualise knee osteoarthritis, its causes and consequences, contributors to pain, and optimal management approaches. PERSPECTIVE: The OACQ is a 36 item, four-domain questionnaire with evidence for construct, structural, and convergent validity, as well as reliability for people with knee osteoarthritis. The OACQ can be used to comprehensively evaluate the conceptual framework of painful knee osteoarthritis.