Psychometric evaluation of the WHODAS 2.0 and prevalence of disability in a Swedish general population.

Background: The World Health Organization Disability Assessment Schedule (WHODAS 2.0) is a generic questionnaire that captures health and disability-related functioning information corresponding to six major life domains: Cognition, Mobility, Self-care, Getting along, Life activities, and Participation. The WHODAS 2.0 is used in a wide range of international clinical and research settings. A psychometric evaluation of WHODAS 2.0, Swedish version, in the general population is lacking, together with national reference data to enable interpretation and comparison. This study aims to evaluate the psychometric properties of the Swedish 36-item version of WHODAS 2.0 and describe the prevalence of disability in a Swedish general population.

Methods: A cross-sectional survey was performed. Internal consistency reliability was assessed with Cronbach's alpha. The construct validity was evaluated with item-total correlation, Pearson's correlation between the WHODAS 2.0 domains and the RAND-36 subscales, analysis of known groups by one-way ANOVA, and analysis of the factor structure by confirmatory factor analysis.

Results: Three thousand four hundred and eighty two adults aged 19-103 years (response rate 43%) participated. Significantly higher degrees of disability were reported by the oldest age group (≥ 80 years), adults with a low level of education, and those on sick leave. Cronbach's alpha was from 0.84 to 0.95 for the domain scores and 0.97 for the total score. The item-scale convergent validity was satisfactory, and the item-scale discriminant validity was acceptable except for the item about sexual activity. The data partially supported the factor structure, with borderline fit indices.

Conclusion: The psychometric properties of the self-administered Swedish 36-item version of the WHODAS 2.0 are comparable to those of other language versions of the instrument. Data of the prevalence of disability in Swedish general population enables normative comparisons of WHODAS 2.0 scores of individuals and groups within clinical practice. The instrument has certain limitations that could be improved on in a future revision. The test-retest reliability and responsiveness of the Swedish version of WHODAS 2.0 for different somatic patient populations remain to be evaluated.