Original Article
Modified WHODAS-II provides valid measure of global disability but filter items increased skewness

https://doi.org/10.1016/j.jclinepi.2007.12.009Get rights and content

Abstract

Objective

The WHODAS-II was substantially modified for use in the World Mental Health Surveys. This article considers psychometric properties and implications of filter items used to reduce respondent burden of the modified WHODAS-II.

Study Design and Setting

Seventeen surveys in 16 countries administered a modified WHODAS-II to population samples (N = 38,934 adults). Modifications included introducing filter questions for four subscales and substituting questions on the number of days activity was limited for the Life Activities domain. We evaluated distributional properties, reliability, and validity of the modified WHODAS-II.

Results

Most respondents (77%–99%) had zero scores on filtered subscales. Lower bound estimates of internal consistency (alpha) for the filtered subscales were typically in the 0.70s, but were higher for the Global scale. Loadings of subscale scores on a Global Disability factor were moderate to high. Correlations with the Sheehan Disability Scale were modest but consistently positive, while correlations with SF-12 Physical Component Summary were considerably higher. Cross-national variability in disability scores was observed, but was not readily explainable.

Conclusions

Internal consistency and validity of the modified WHODAS-II was generally supported, but use of filter questions impaired measurement properties. Group differences in modified WHODAS-II disability scores may be compared within, but not necessarily across, countries.

Introduction

The International Classification of Functioning, Disability, and Health [1] organizes the consequences of disease into four dimensions: body functions and structure (symptoms and impairment); activities; participation, and environmental factors [2]. The World Health Organization Disability Assessment Schedule (WHODAS-II) is a disability instrument designed based on the International Classification of Functioning, Disability, and Health framework, assessing six domains of functioning in daily life. The WHODAS-II is a standardized measurement of disability for use in diverse cultural settings, translated into 16 languages to date [3], [4]. The instrument allows group comparisons of global disability and domain-specific disability for physical and mental disorders. The WHODAS-II domains include: Understanding and Communicating; Getting Around; Self Care; Getting Along With Others; Life Activities; and Participation in Society [3], [4]. Initial psychometric analyses carried out by the WHO indicated that the WHODAS-II domains yielded a two-level hierarchical structure in which individual items load onto one of six domains, which in turn load onto a Global Disability latent variable. The WHODAS-II web site reports that all six domains have factor loadings of at least 0.7 on a Global Disability latent variable [3].

There is a growing literature evaluating psychometric properties of the WHODAS-II [5], [6], [7], [8], [9], [10], [11], [12], [13]. Among primary care patients with depression or back pain, Chwastiak and Von Korff [5] reported high internal consistency for all domains except Self-Care (whose alphas were in the vicinity of 0.65), and good responsiveness to change. They also found good convergent validity in relation to the SF-36, the Work Limitations Questionnaire and condition-specific severity scales. Perini et al. [6] found that the WHODAS-II was associated with symptom change among persons with anxiety disorders. Chisolm et al. [7] reported moderate-to-high correlations with SF-36 scales, adequate test–retest reliability, and good internal consistency for all domains except Getting Along With Others. Overall, initial evaluation of the WHODAS-II suggests acceptable internal consistency, test–retest reliability, convergent validity, and responsiveness to change.

This article assesses the psychometric performance of the WHODAS-II as modified for the World Mental Health (WMH) Surveys [14]. The WMH Survey Initiative is a series of population surveys concerning mental disorders conducted in participating countries on a global scale. Substantial changes to the WHODAS-II were made for the WMH surveys. Although these changes were deemed necessary to achieve the overall goals of the WMH surveys, they have the potential to alter the psychometric properties of the WHODAS-II. The purpose of this article is to assess the psychometric properties of the modified WHODAS-II including: (1) internal consistency of the five retained domains, (2) convergent validity with the Sheehan Disability Scale and SF-12 Physical and Mental Component Summary scores, and (3) assessing with confirmatory factor analysis whether the five retained domain scores have high loadings on a global disability latent variable. We also present population normative data for a Global Disability Scale based on the five domain scores. Because the WMH version of the WHODAS-II will be used to assess functional disability in reporting WMH survey results, understanding its strengths and limitations is important for interpretation of disability studies reported by the WMH surveys. The use of filter questions is an increasingly common method for reducing respondent burden in multipurpose surveys. This article considers how well the filter questions introduced for the WHODAS-II subscales performed.

Section snippets

Methods

Samples: The analyses reported here are based on seventeen surveys carried out in 16 countries in the Americas (Colombia, Mexico, United States), Europe (Belgium, France, Germany, Italy, Netherlands, Spain, Ukraine), the Middle East/Africa (Israel, Lebanon, Nigeria), Asia (Japan, separate surveys in Beijing and Shanghai in the People's Republic of China), and the South Pacific (New Zealand). All surveys were based on multistage, clustered area probability household samples in 2001–2004. All

Results

Table 1 provides the (weighted) percent of the population for each survey that had a nonzero score for each of the five domain subscales, and for the Global Disability Scale. Persons giving a negative answer to the filter question for the first four domains would always have a zero score. The results in Table 1 show that the large majority of respondents had zero scores for each of the domains, particularly for the four domains with filter questions. Self-Care and Getting Along With Others

Discussion

The modifications to the WHODAS-II implemented in the WMH Surveys produced a shorter test thereby reducing respondent burden. Reduced respondent burden appeared to have come at some cost in terms of reduced internal consistency along with a large proportion of respondents having zero scores. Validity coefficients were also not as high as indicated by prior research, except for the SF-12 Physical Component Summary score which showed a high correlation with the modified WHODAS-II Global

Acknowledgments

The surveys included in this report were carried out in conjunction with the World Health Organization World Mental Health (WMH) Survey Initiative. We thank the WMH staff for assistance with instrumentation, fieldwork, and data analysis. These activities were supported by the United States National Institute of Mental Health (R01MH070884), the John D. and Catherine T. MacArthur Foundation, the Pfizer Foundation, the U.S. Public Health Service (R13-MH066849, R01-MH069864, and R01 DA016558), the

References (22)

  • P. Gallagher et al.

    Levels of ability and functioning: using the WHODAS II in an Irish context

    Disabil Rehabil

    (2004)
  • Cited by (0)

    View full text