Psychometric properties of the twelve item World Health Organization Disability Assessment Schedule II (WHO-DAS II) in Spanish primary care patients with a first major depressive episode.

BACKGROUND: Psychometric information on the World Health Organization Disability Assessment Schedule II (WHO-DAS II) in depressive primary care (PC) patients is scarce and has been obtained with the 36-item version of the instrument. The main objective of this study was to analyse the dimensionality, internal consistency and construct validity of the 12-item WHO-DAS II in a large sample of Spanish PC patients with a first diagnosed major depressive episode. METHOD: Data were collected between December 2006 and July 2007. A total of 3615 adult (18 years or older) PC patients from 17 regions of Spain with a first diagnosed major depressive episode participated in the study. The 12-item WHO-DAS II and a battery of instruments assessing sociodemographic characteristics, depression severity (PHQ-9), quality of life (EQ-5D) and chronic health conditions were administered by the family physician during the consultation. RESULTS: The principal component analysis and the subsequent confirmatory factor analysis indicated that the 12-item WHO-DAS II is one-dimensional. The instrument showed adequate internal consistency (alpha=0.89) and construct validity because it was significantly associated with quality of life and depression severity (convergent validity) and was able to discriminate between patients on sick leave and those that were working (discriminative validity). LIMITATIONS: The test-retest reliability and sensitivity to change of the instrument was not examined due to the cross-sectional design of the study. CONCLUSIONS: The 12-item WHO-DAS II is a reliable, valid and useful tool for assessing overall disability in PC patients with depression.