Research reportPsychometric 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
Introduction
Lehman et al. (2002) pointed out that psychiatric symptoms and disability are usually inter-correlated, but not equivalent. Thus, a patient can experience several symptoms that result in little disability, whereas another patient can report severe disability with relatively few psychiatric symptoms. Moreover, disability may even vary among individuals reporting similar levels of psychiatric symptoms (e.g. Huang et al., 2006), suggesting the importance to measure symptoms and disability separately from each other (Üstün and Chatterji, 1998).
One of the most comprehensive measures of disability is the World Health Organization Disability Assessment Schedule II (WHO-DAS II; WHO, 2000). It is a multidimensional instrument developed by the Assessment, Classification, and Epidemiology group (ACE), a unit in the Global Programme on Evidence for Health Policy (GPE) at the World Health Organization headquarters in Geneva, Switzerland. The instrument comprises 36 items that capture six domains: understanding and communicating, getting around, self-care, getting along with people, life activities, and participation in society. These domains reflect two dimensions of disability according to the International Classification of Functioning, Disability and Health (ICF. WHO, 2001) model: activity limitations (understanding and communicating; getting around; and self-care) and participation (getting along with others; life activities; and participation in society). The main advantages of this instrument over other disability measures are the next: it was cross-culturally developed and field tested in 16 languages in 14 different countries, it is compatible with an international classification system (the International Classification of Functioning, Disability and Health, ICF; WHO, 2001) and treats all disorders at parity when establishing the level of functioning. A shorter version of the instrument with 12 items was also developed, which is recommendable for epidemiological studies and routine outcome assessment or when domain-specific information regarding functioning is not required.
Several studies have extensively analysed the psychometric properties of the 36-item WHO-DAS II in patients suffering diverse chronic health conditions, demonstrating that the instrument possesses an excellent internal consistency, as well as an adequate construct validity (Baron et al., Baron et al., 2008, Chávez et al., 2005, Chisolm et al., 2005, Chwastiak and Von Korff, 2003, Hudson et al., 2008, McKibbin et al., 2004, Pösl et al., 2007, Vázquez-Barquero et al., 2000). However, although major depression is one of the disorders with highest social costs and greatest negative impact on subjects' well-being (Druss et al., 2000, Moussavi et al., 2007, Ormel et al., 2008, Paykel et al., 2005, Üstün et al., 2004), there is little information concerning the usefulness, reliability and validity of the WHO-DAS II in patients suffering this disorder. As far as we know, the only published psychometric reports were made by Chwastiak and Von Korff (2003) and Pösl et al. (2007), who administered the 36-item WHO-DAS II to a small sample of depressive primary care patients and to a heterogeneous sample with different chronic health conditions (including depressive disorder), respectively. In both cases the instrument showed an excellent internal consistency, convergent validity and sensitivity to change after treatment for the disorder. To sum up, the available psychometric information on the WHO-DAS II in depressive patients is scarce and obtained with the 36-item version of the instrument.
The main objective of the present study is to analyse the psychometric properties of the 12-item WHO-DAS II in a large sample of PC patients with a first diagnosed major depressive episode. More specifically, using the classical test theory as framework, we analysed the instrument's factor structure, internal consistency and construct validity.
Section snippets
Method
In the present work we utilized the ERASMAP dataset. The ERASMAP was a cross-sectional observational study carried out in 874 PC centres from Spain designed to identify the sociodemographic and clinical factors associated to diagnostic delay in a first time diagnosed major depressive episode. A total of 1210 family physicians agreed to participate in the study. The protocol was approved by the Clinical Research and Ethics Committee of the University Hospital La Princesa (Madrid, Spain).
Results
Sociodemographic characteristics of the total sample are presented in Table 1. The participants ranged in age from 19 to 94 years (M = 50; SD = 13.89) and 67.33% of the sample were female.
Discussion
To our knowledge, this is the first study that has examined the factor structure and psychometric properties of the 12-item WHO-DAS II in depressive PC patients. One of the main strengths is that the recruited cohort was large and included patients geographically, culturally, and economically diverse. Notwithstanding, our results should be interpreted with caution because we did not use a structured clinical interview (e.g. the SCID-I or the Mini Neuropsychiatric Diagnostic Interview) to assess
Role of funding source
This study was funded by H. Lundbeck A/S. Lundbeck A/S was responsible for field work and collection of data. They did not have any role in the analysis and interpretation of data, in the writing of the manuscript, and in the decision to submit the paper for publication.
Conflict of interest
José L. Ayuso-Mateos, Josep M. Haro and Miquel Roca received economic compensation for the design coordination of the study. Other authors declare that they have no conflicts of interests.
Acknowledgements
Juan V. Luciano and Ana Fernández are grateful to the “Spanish Ministry of Health, Instituto de Salud Carlos III” (Red RD06/0018/0017) for a postdoctoral and a predoctoral contract, respectively. José L. Ayuso-Mateos' work was supported in part by the “Spanish Ministry of Health, Instituto de Salud Carlos III” (PI050036) and the CIBERSAM. We would like to thank Dr. José M. Tomás (University of Valencia, Spain) for his advice on confirmatory factor analyses and advice in running of the EQS
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