An item analysis according to the Rasch model of the German 12-item WHO Disability Assessment Schedule (WHODAS 2.0)

Purpose The World Health Organization Disability Assessent Schedule 2.0 (WHODAS 2.0) assesses disability in individuals irrespective of their health condition. Previous studies validated the usefulness of the WHODAS 2.0 using classical test theory. This study is the first investigating the psychometric properties of the 12-items WHODAS 2.0 in patients with cancer using item analysis according to the Rasch model. Methods In total, 350 cancer patients participated in the study. Rasch analysis of the 12-items version of the WHODAS 2.0 was conducted and included testing unidimensionality, local independence, and testing for differential item functioning (DIF) with regard to age, gender, type of cancer, presence of metastases, psycho-oncological support, and duration of disease. Results After accounting for local dependence, which was mainly found across items of the same WHODAS domain, satisfactory overall fit to the Rasch model was established (chi(2) = 36.14, p = 0.07) with good reliability (PSI = 0.82) and unidimensionality of the scale. DIF was found for gender (testlet 'Life activities') and age (testlet 'Getting around/Self-care'), but the size of DIF was not substantial. Conclusion Overall, the analysis results according to the Rasch model support the use of the WHODAS 2.0 12-item version as a measure of disability in cancer patients.