Evaluation of the World Health Organization Disability Assessment Schedule II (WHO DAS II) - German Version

ABSTRACT Backgroud: The World Health Organization Disability Assessment Schedule II (WHODAS II) is a new measure of functioning and disability that is conceptually compatible with the International Classification of Functioning, Disability, and Health (ICF). In contrast to other measures of health status, the WHODAS II is based on an international classification system, it is designed to be applicable across different cultures, and it treats all disorders at parity when determining the level of functioning. Objective: The general objective of this study is to investigate whether the WHODAS II – German version – is a useful instrument for measuring functioning and disability in patients with musculoskeletal conditions, cardiovascular and general internal conditions, stroke, breast cancer and depressive disorder. Specific objectives are to assess its psychometric properties reliability (internal consistency, Cronbach's Alpha), validity (factor analysis of dimensionality, convergent validity, discriminant validity), and sensitivity to change (effect size and standardized response mean), to determine to what extent the WHODAS II correlates with a traditional generic instrument for measuring Health Related Quality of Life, the SF-36, and to define its sensitivity to change after a rehabilitative intervention in relation to that other instrument. Methods: Patients with musculoskeletal conditions, cardiovascular and general internal conditions, stroke, breast cancer and depressive disorder participated. The patients completed the questionnaires WHODAS II and SF-36. After a rehabilitation treatment the same patients completed these questionnaires again in order to assess sensitivity to change. Analyses of measurement properties were conducted. Sensitivity to change was calculated by the effect size (ES) and standardized response mean (SRM). Results: Mean score on the WHODAS II is 21.98 (SD 14.32) for musculoskeletal conditions, 18.47 (SD 15.32) for internal conditions, 38.72 (SD 24.79) for stroke, 23.84 (SD 16.61) for breast cancer, and 44.56 (SD 18.95) for depressive disorder. High reliability is obtained. For the most part, the results of the scale replication confirm the determined six domains of the questionnaire. For the domain Activities, a clear distinction between work und household activities is apparent in both musculoskeletal and internal conditions. The correlations found in comparison to the SF-36 indicated that the WHODAS II (German version) measured indeed the expected constructs. The effect sizes of the WHODAS II Total Score range from 0.163 to 0.687 depending on the subgroup; effect sizes of the SF-36 summary scores from 0.025 to 1.395, respectively. In terms of patients reporting an improvement of general health status, effect sizes are accordingly higher (0.220 to 0.915 for the WHODAS II; 0.083 to 2.023 for the SF-36). Conclusion: The WHODAS II (German version) is a useful instrument for measuring functioning and disability in patients with musculoskeletal diseases, internal diseases, stroke, breast cancer and depressive disorder. It is reliable and valid and shows similar sensitivity to change scores as the SF-36 in the accordingly subscales.