Measuring disability experienced by adults living with HIV: assessing construct validity of the HIV Disability Questionnaire using confirmatory factor analysis
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OBJECTIVES: To assess the construct validity of the HIV Disability Questionnaire (HDQ), a self-administered questionnaire that describes the presence, severity and episodic nature of disability experienced by people living with HIV. DESIGN: We conducted a confirmatory factor analysis. We hypothesised that domains in the HDQ characterised six dimensions of disability, each represented by HDQ items: physical symptoms and impairments (20 items); cognitive symptoms and impairments (3 items); mental and emotional health symptoms and impairments (11 items); uncertainty (14 items); difficulties with day-to-day activities (9 items) and challenges to social inclusion (12 items). We developed a measurement model to test these hypotheses. We used maximum likelihood methods of estimation to determine model fit. We considered a threshold for the Root Mean Square Error of Approximation (RMSEA) of <0.05 as an indication of overall goodness of model fit. We considered variables with factor loadings of >0.30 as representing a given domain of disability. SETTING: We recruited adults with HIV from hospital clinics, AIDS service organisations and a specialty hospital in Ontario. PARTICIPANTS: Of the 361 adults with HIV who completed the HDQ, 80% were men, 36% were 50 or older and 77% reported living with at least two concurrent health conditions in addition to HIV. OUTCOME MEASURES: We administered the HDQ followed by a demographic questionnaire. RESULTS: The model achieved good overall fit as indicated by a RMSEA of 0.030 (90% CI 0.028 to 0.033). All HDQ items represented our hypothesised dimensions of disability (factor loadings >0.30). Factor loadings ranged from 0.34 to 0.90. Domains of disability correlated with each other ranging from r=0.47 (between difficulties with day-to-day activities and uncertainty) to r=0.88 (between mental-emotional health challenges and challenges to social inclusion). CONCLUSIONS: The six domain structure of the HDQ demonstrated construct validity when administered to adults living with HIV.
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