Validation of a Spanish version of the Health Assessment Questionnaire-II to assess Mexican patients' physical function with rheumatoid arthritis.

OBJECTIVE: To evaluate the validity, reliability, and performance of the Health Assessment Questionnaire-II (HAQ-II) Spanish version questionnaire to measure physical function. METHODS: A cross-sectional study of 496 patients with rheumatoid arthritis (RA), distributed in 2 samples. The construct validity was evaluated employing the confirmatory factor analysis (CFA) and the validity based on the relationship with other variables. Cronbach's alpha (α) and McDonald's omega (ω) coefficient were used to determine reliability. Item performance was analysed by fitting different models of item response theory (IRT). RESULTS: The one-factor model presented a poor fit in the CFA; an exploratory factor analysis (AFE) was carried out, which suggested a 2-factor structure. The CFA in the second sample confirmed that the second-order model had a good fit to the data. The general factor explained more than 70% of the variance. The reliability indices showed adequate internal consistency (α = .92-.95; ω = .88-.93). Ninety-three percent of the contrasting hypotheses about the relationship of the HAQ-II scores with other variables were confirmed, demonstrating their convergent, divergent, and known group validity. The multidimensional graduated response model was the one that best predicted person's interaction with the items. CONCLUSION: The Spanish version of the HAQ-II presents adequate validity and reliability for measuring Mexican patients' physical function with RA.