Satisfactory cross cultural equivalence of the Dutch WOMAC in patients with hip osteoarthritis waiting for arthroplasty
- L D Roorda1,2,
- C A Jones3,
- M Waltz4,
- G J Lankhorst1,2,
- L M Bouter2,
- J W van der Eijken5,
- W J Willems6,
- I C Heyligers7,
- D C Voaklander8,
- K D Kelly8,
- M E Suarez-Almazor9
- 1Department of Rehabilitation Medicine, VU University Medical Centre, Amsterdam, The Netherlands
- 2Institute for Research in Extramural Medicine, VU University Medical Centre, Amsterdam, The Netherlands
- 3Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB, Canada
- 4Rheumatology Department, St Willibrord Hospital, Emmerich, Germany
- 5Department of Orthopaedic Surgery, Onze Lieve Vrouwe Gasthuis, Amsterdam, The Netherlands
- 6Department of Orthopaedic Surgery, Medisch Centrum Alkmaar, Alkmaar, The Netherlands
- 7Department of Orthopaedic Surgery, VU University Medical Centre, Amsterdam, The Netherlands
- 8British Columbia Rural and Remote Health Research Institute, College of Arts, Social and Health Sciences, University of Northern British Columbia, Prince George, BC, Canada
- 9Section of Health Services Research, Department of Medicine, Baylor College of Medicine, Houston, TX, USA
- Correspondence to:
Dr L D Roorda
VU University Medical Centre, Department of Rehabilitation Medicine, PO Box 7057, 1007 MB Amsterdam, The Netherlands;
- Accepted 12 May 2003
Background: Cross cultural validity is of vital importance for international comparisons.
Objective: To investigate the validity of international Dutch-English comparisons when using the Dutch translation of the Western Ontario and McMaster Universities osteoarthritis index (WOMAC).
Patients and Methods: The dimensionality, reliability, construct validity, and cross cultural equivalence of the Dutch WOMAC in Dutch and Canadian patients waiting for primary total hip arthroplasty was investigated. Unidimensionality and cross cultural equivalence was quantified by principal component and Rasch analysis. Intratest reliability was quantified with Cronbach’s α, and test-retest reliability with the intraclass correlation coefficient. Construct validity was quantified by correlating sum scores of the Dutch WOMAC, Arthritis Impact Measurement Scales (Dutch AIMS2), Health Assessment Questionnaire (Dutch HAQ), and Harris Hip Score (Dutch HHS).
Results: The WOMAC was completed by 180 Dutch and 244 English speaking Canadian patients. Unidimensionality of the Dutch WOMAC was confirmed by principal component and Rasch analysis (good fit for 20/22 items). The intratest reliability of the Dutch WOMAC for pain and physical functioning was 0.88 and 0.96, whereas the test-retest reliability was 0.77 and 0.92, respectively. Dutch WOMAC pain sum score correlated 0.69 with Dutch HAQ pain, and 0.39 with Dutch HHS pain. Dutch WOMAC physical functioning sum score correlated 0.46 with Dutch AIMS2 mobility, 0.62 with Dutch AIMS2 walking and bending, 0.67 with Dutch HAQ disability, and 0.49 with Dutch HHS function. Differential item functioning (DIF) was shown for 6/22 Dutch items.
Conclusions: The Dutch WOMAC permits valid international Dutch-English comparisons after correction for DIF.
- AIMS, Arthritis Impact Measurement Scale
- CI, confidence interval
- DIF, differential item functioning
- HAQ, Health Assessment Questionnaire
- HHS, Harris Hip Score
- HR QOL, health related quality of life
- ICC, intraclass correlation coefficient
- OA, osteoarthritis
- SD, standard deviation
- SE, standard error
- THA, total hip arthroplasty
- WOMAC, Western Ontario and McMaster Universities osteoarthritis index
No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organisation with which the authors are associated.