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

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.