title: 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: OBJECTIVE
  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).
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  The WOMAC-pf is a unidimensional measure of physical functioning in patients with LOSP and PD, in addition to its established use in OA. [
  
  
  CONCLUSIONS
  • Disability 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 bea 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.]
authors.affiliation: Institute for Applied Health Research and School of Health, Glasgow Caledonian University ,  Glasgow, Scotland ,  United Kingdom.
authors.forename: Martijn P M
authors.initials: MP
authors.lastname: Steultjens
authors.forename: Janneke
authors.initials: J
authors.lastname: Stolwijk-Swüste
authors.forename: Leo D
authors.initials: LD
authors.lastname: Roorda
authors.forename: Annet J
authors.initials: AJ
authors.lastname: Dallmeijer
authors.forename: Gabriella M
authors.initials: GM
authors.lastname: van Dijk
authors.forename: Bart
authors.initials: B
authors.lastname: Post
authors.forename: Joost
authors.initials: J
authors.lastname: Dekker
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D010300:Parkinson Disease / Q000503:physiopathology*; D011051:Poliomyelitis / Q000503:physiopathology*; D025341:Principal Component Analysis; D011594:Psychometrics / Q000706:statistics & numerical data*; D011788:Quality of Life / Q000523:psychology; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards