Feasibility and psychometric properties of the German 12-item WHO Disability Assessment Schedule (WHODAS 2.0) in a population-based sample of patients with myocardial infarction from the MONICA/KORA myocardial infarction registry.

Background: The World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0) provides a standardized assessment of functioning and disability in individuals with any kind of disease. So far, data on feasibility and psychometric properties of the 12-item WHODAS 2.0 in patients with acute myocardial infarction (AMI) are not available. Thus, the objective of this study was to investigate feasibility and psychometric properties of this questionnaire in a population-based sample of persons with AMI.Methods: The sample consisted of 2077 persons (age 35-85 years) with AMI from the population-based MONICA/KORA Myocardial Infarction Registry, Augsburg, Germany, who responded to a postal follow-up survey in 2011. Feasibility was assessed by the number of missing WHODAS 2.0 items and analyzed using multivariate logistic regression modeling. Psychometric properties were determined using Rasch analysis. It included testing of unidimensionality, monotonicity and local independency, Partial Credit Model (PCM) fitting, and testing for Differential Item Functioning (DIF). Concurrent validity was tested by a linear additive model predicting the WHODAS disability score based on a number of independent variables.Results: For 96% of the subjects, the WHODAS disability score could be computed. Incomplete questionnaires were significantly more common in older persons (Odds ratio (OR) 1.03, 95% confidence interval (CI) 1.01-1.05) and persons with bad/very bad self-rated health (OR 2.55, 95% CI 1.28-5.06). The assumptions of Rasch modeling were fulfilled. The PCM revealed disordered thresholds for nine of the 12 items. However, it was possible to achieve a correct order of thresholds by collapsing the five response options to three. The item thresholds covered the whole range of the continuum, indicating that items are appropriate to differentiate between persons across the whole continuum of disability. No DIF was detected for any of the tested variables such as age, sex, and education. Significantly higher disability scores were found in persons with comorbidities and impaired overall health status, confirming concurrent validity.Conclusions: The 12-item WHODAS 2.0 is a feasible, nonbiased, and valid instrument for application in persons with AMI. Shortcomings refer to unordered thresholds of most items. Further studies are required in order to confirm these findings