Rasch analysis of the western ontariomcmaster (WOMAC) osteoarthritis index: results from community and arthroplasty samples

Davis, A.M.; Badley, E.M.; Beaton, D.E.; Kopec, J.; Wright, J.G.; Young, N.L.; Williams, J.I.

doi:10.1016/S0895-4356(03)00179-3

« Previous Next »Journal of Clinical Epidemiology
Volume 56, Issue 11 , Pages 1076-1083, November 2003

Rasch analysis of the western ontariomcmaster (WOMAC) osteoarthritis index: results from community and arthroplasty samples

A.M. Davis
- Departments of Physical Therapy, Graduate Department of Rehabilitation Science and Health Policy, Management and Evaluation (Program in Clinical Epidemiology and Health Services Research), Toronto Rehabilitation Institute and the University of Toronto, Room 1119, 550 University Avenue, Toronto, ON M5G 2A2, Canada
- Corresponding author. Tel.: 416-597-3422, ext. 3478; fax: 416-597-3031.
E.M. Badley
- Arthritis Community Research and Evaluation Unit, Graduate Department of Public Health Science, University Health Network, University of Toronto, Toronto Western Research Institute, 399 Bathurst Street, MP10-310, Toronto, ON M5T 2S8, Canada
D.E. Beaton
- Institute for Work and Health, Mobility Program and Clinical Research, Departments of Occupational Therapy, Graduate Department of Health Policy, Management and Evaluation (Program in Clinical Epidemiology and Health Services Research), University of Toronto, St. Michael's Hospital, 30 Bond Street, Toronto, ON M5B 1W8, Canada
J. Kopec
- Arthritis Research Centre of Canada and the Department of Health Care and Epidemiology, University of British Columbia, 895 West 10th Avenue, Vancouver, BC V5Z 1L7, Canada
J.G. Wright
- Department of Surgery and Population Health Science, Hospital for Sick Children, Graduate Department of Health Policy, Management and Evaluation (Program in Clinical Epidemiology and Health Services Research), University of Toronto, 555 University Avenue, Toronto, ON M5G 1X8, Canada
N.L. Young
- Community Health Systems Resource Group, Hospital for Sick Children, Departments of Pediatrics and Physical Therapy, Graduate Department of Rehabilitation Science and Health Policy (Program in Clinical Epidemiology and Health Services Research), University of Toronto, 555 University Avenue, Toronto, ON M5G 1X8, Canada
J.I. Williams
- Toronto Rehabilitation Institute and the Institute for Clinical and Evaluative Sciences, Sunnybrook and Women's College Health Sciences Centre, Public Health Science, University of Toronto, 550 University Avenue, Toronto, ON M5G 2A2, Canada

Accepted 1 June 2003.

Abstract

Background and objective

This study is based on secondary analysis of Western Ontario McMaster Osteoarthritis Index (WOMAC) data from a community sample over 55 years and total hip or knee arthroplasty samples presurgery and 1-year postoperative.

Methods

The WOMAC data were evaluated by Rasch analysis. Data were considered to fit the Rasch mathematical model for the pain and physical dimensions of the WOMAC if unidimensionality was confirmed by principle component analysis of the subscale and the residuals from the Rasch analysis, infit and outfit statistics were in the range of 0.80 to 1.20; if there was no differential item functioning based on gender or hip vs. knee subjects; and, if there was stability of the item logits across the three data samples.

Results

A three-item pain dimension (excluding night pain and pain on standing) and a 14-item physical dimension (excluding heavy domestic duties, getting in and out of the bath and getting on and off the toilet) fit the Rasch model based on these criteria.

Conclusion

In evaluating existing health status questionnaires using Rasch methodology, it is important to evaluate relevant patient samples and longitudinal data when the measure is intended to evaluate change in status. By these criteria, a modified WOMAC questionnaire fits the Rasch model and has interval-level scaling properties.

Keywords: WOMAC, Rasch analysis, Longitudinal data, Joint arthroplasty, Arthritis, Outcome measurement