Anàlisi factorial confirmatòria per a variables categòriques: Aplicació al qüestionari de discapacitat WHODAS-II

Abstract

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.