Scale Development of the Osteoarthritis Conceptualisation Questionnaire: Phase 3 Convergent Validity and Test-retest Reliability.

Abstract

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 poor, although all OACQ subscales showed unidimensionality. Person fit was below the acceptable threshold for two subscales; however, sensitivity analysis revealed no specific cause for this misfit. Internal consistency was good for all subscales, and DIF was consistent with expected associations between measures. Rasch findings were supported in the confirmatory sample. The OACQ had correlations with related measures supportive of convergent validity and demonstrates 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.