Validation of the World Health Organization disability assessment schedule II (WHODAS-II) in patients with osteoarthritis.

The objective of this study is to test the reliability and validity of WHODAS-II (Turkish version) for the assessment of disability in patients with osteoarthritis. This study is designed as follows: the internal construct validity of WHODAS-II in patients with knee osteoarthritis was assessed by Rasch analysis, and external construct validity by association with the Western Ontario and McMaster Universities Index of Osteoarthritis (WOMAC) and the Nottingham Health Profile (NHP); reliability was tested by internal consistency, intra-class correlation coefficient (ICC) and test-retest ICC. Our study presents the results of 225 outpatients assessed with mean age 58.4 years (SD 11.1) of whom 80.9% were female. Cronbach's α, ICC, and test-retest ICC values for the six subscales of WHODAS-II varied between 0.71 and 0.94, 0.71 and 0.94, and 0.87 and 0.97, respectively. Rasch analysis of WHODAS-II indicated that after adjustment for local dependency, satisfactory fit was achieved. Two separate 'activities' and 'participation' components could also be identified. External construct validity of the scale was confirmed with expected correlations with WOMAC and NHP. This study concludes that WHODAS-II provides a reliable and valid health status instrument for measuring disability and components of 'activities' and 'participation' in patients with osteoarthritis. Thus, it provides the opportunity to model the consequences of disease according to the International Classification of Functioning, Disability and Health framework.