An item response theory analysis of EQ-5D-5L questionnaire’s performance in patients with hip or knee osteoarthritis

Purpose The aim of this study was to conduct a comprehensive analysis of the item-level psychometric properties of the Spanish EQ-5D-5L questionnaire in patients with hip or knee osteoarthritis (OA) using item response theory. Methods The study included 758 patients with hip or knee OA who completed the EQ-5D-5L questionnaire. The EQ-5D-5L contains five questions (mobility (MOB), self-care (SC), usual activities (UA), pain/discomfort (PD), and anxiety/depression (AD)) from which a utility index is derived. A complete validation was performed, including graded response modelling to study item functioning and the assessment of differential item functioning considering sex and affected joint. Results The graded response model results showed that all items were good at discriminating the latent trait. Items on MOB and UA had the greatest discriminating power, also covering the widest range of the trait. AD item had the least discriminating power and was the one that covered the narrowest range of the trait. PD item was more apparent at lower levels of severity and SC item at higher levels. Some degree of sex-related differential item functioning was detected in AD item, being somewhat more apparent at higher levels of severity in males than females. Conclusions The graded response model results support the adequate functioning of all the items on the EQ-5D-5L in these patients, providing more evidence of its validity in OA. Therefore, the EQ-5D-5L could be of interest in clinical research and routine practice in the orthopaedic community for measuring health-related quality of life.