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Abstract:
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Objective: To describe the methodology of Confirmatory Factor Analyis for categorical items and to apply this methodology to evaluate the factor structure and invariance of the WHO-Disability Assessment Schedule (WHODAS-II) questionnaire, developed by the World Health
Organization.
Methods: Data used for the analysis come from the European Study of Mental Disorders
(ESEMeD), a cross-sectional interview to a representative sample of the general population of 6 european countries (n=8796). Respondents were administered a modified version of the
WHODAS-II, that measures functional disability in the previous 30 days in 6 different
dimensions: Understanding and Communicating; Self-Care, Getting Around, Getting Along with
Others, Life Activities and Participation. The questionnaire includes two types of items: 22
severity items (5 points likert) and 8 frequency items (continuous). An Exploratory factor
analysis (EFA) with promax rotation was conducted on a random 50% of the sample. The
remaining half of the sample was used to perform a Confirmatory Factor Analysis (CFA) in
order to compare three different models: (a) the model suggested by the results obtained in the
EFA; (b) the theoretical model suggested by the WHO with 6 dimensions; (c) a reduced model
equivalent to model b where 4 of the frequency items are excluded. Moreover, a second order
factor was also evaluated. Finally, a CFA with covariates was estimated in order to evaluate
measurement invariance of the items between Mediterranean and non-mediterranean countries.
Results: The solution that provided better results in the EFA was that containing 7 factors. Two
of the frequency items presented high factor loadings in the same factor, and one of them
presented factor loadings smaller than 0.3 with all the factors. With regard to the CFA, the
reduced model (model c) presented the best goodness of fit results (CFI=0.992,TLI=0.996,
RMSEA=0.024). The second order factor structure presented adequate goodness of fit (CFI=0.987,
TLI=0.991, RMSEA=0.036). Measurement non-invariance was detected for one of the items of the
questionnaire (FD20 ¿ Embarrassment due to health problems).
Conclusions: AFC confirmed the initial hypothesis about the factorial structure of the WHODAS-II in 6
factors. The second order factor supports the existence of a global dimension of disability. The use of 4
of the frequency items is not recommended in the scoring of the corresponding dimensions. |
