Dimensionality, reliability, and validity of the revised fibromyalgia impact questionnaire in two Spanish samples

The present study attempted to fill a research gap by performing the first dimensionality analysis of the Revised Fibromyalgia Impact Questionnaire (FIQR) using exploratory and confirmatory techniques. A second objective was to report on the reliability and construct validity of the FIQR in Spanish patients.

FIQR data from a sample of adult fibromyalgia patients (n = 113) were analyzed using principal components analysis (PCA). Subsequently, a set of confirmatory factor analyses (CFAs) was conducted in another sample (n = 179) to analyze the goodness of fit of various factor models. FIQR reliability was assessed by computing Cronbach's alpha and coefficient H. Construct validity was evaluated by comparing the FIQR scores of participants categorized by employment status.

According to the PCA, the FIQR structure might be described as having 1 global factor of functional impairment. Although subsequent CFAs confirmed that 1 factor accounted for the greatest proportion of common variance in the FIQR items, a confirmatory bifactor analysis indicated that the items were multidimensional because of their simultaneous significant loading on specific factors. The Cronbach's alpha values of the FIQR domains were very good (>0.80) and the H estimate for the FIQR total score was excellent (0.93). Overall, the FIQR domains were able to distinguish between patients differing in employment status (working outside the home versus on sick leave).

Our results indicate that the Spanish version of the FIQR has a complex factor structure, has excellent reliability, and shows good construct validity.