WOMAC-pf as a measure of physical function in patients with Parkinson’s disease and late-onset sequels of poliomyelitis: unidimensionality and item behaviour

Abstract

Purpose: To assess psychometric properties of the Western Ontario and MacMasters Universities Osteoarthritis Index (WOMAC)-pf, an osteoarthritis (OA)-specific questionnaire used to establish the level of physical functioning in patients with late-onset sequels of poliomyelitis (LOSP) and Parkinson’s disease (PD). Study design and setting: Unidimensionality (using principal component analyses [PCA] and Rasch analyses) was separately established for three diagnostic groups: OA (n = 288), LOSP (n = 168) and PD (n = 200). Additionally, differential item functioning (DIF) among the three diagnostic groups was assessed using ordinal regression (Polytomous Universal Model) analyses. Baseline data were used from an ongoing cohort study of these three patient populations. Results: Unidimensionality was adequate, with all items loading on the first principal component. The Rasch analyses revealed that item fit was generally good. Uniform and non-uniform DIF were found to be present among the three diagnostic groups in three and one of the 17 physical functioning subscale (WOMAC-pf) items, respectively. Conclusion: The WOMAC-pf is a unidimensional measure of physical functioning in patients with LOSP and PD, in addition to its established use in OA.Implications for RehabilitationDisability in physical functioning related to mobility (walking, stair climbing, etc.) is a common feature of many chronic diseases, including osteoarthritis, late-onset sequels of poliomyelitis and Parkinson’s disease.In this study, the Western Ontario and MacMasters Universities Osteoarthritis Index-pf was shown to be a useful and adequate tool to assess physical functioning in these patient groups.The study highlighted that, despite differences in diagnosis, history and course of the disease, patients with different conditions experience similar disabilities in their physical functioning.