Psychometric evaluation of the Norwegian version of the Revised Fibromyalgia Impact Questionnaire

Abstract

Objectives: The Revised Fibromyalgia Impact Questionnaire (FIQ-R) is a composite questionnaire covering key domains of fibromyalgia disease burden. This study aimed to translate the FIQ-R into Norwegian, to assess face, content, and criterion validity, and to evaluate the psychometric properties of the Norwegian FIQ-R using Rasch analysis, in a sample of adults with fibromyalgia.

Method: The FIQ-R was translated into Norwegian following established methodology in collaboration with patient research partners. Participants attending a patient education session for people with chronic musculoskeletal pain were asked to complete, anonymously, the translated FIQ-R, Fibromyalgia Self-reported Diagnostic Criteria (FSDC), 36-item Short Form Health Survey (SF-36), and Modified Health Assessment Questionnaire (MHAQ). Fibromyalgia cases were identified according to the FSDC. Correlations between FIQ-R, MHAQ, and SF-36 were calculated. Rasch analysis was performed.

Results: In total, 241 participants (96.3% female) were classified as having fibromyalgia according to the FSDC. The translated FIQ-R had acceptable face and content validity. The correlation coefficients were moderate between FIQ-R and SF-36, and strong between FIQ-R and MHAQ. The FIQ-R formed a multidimensional scale, indicating two subscales: FIQ-R function and FIQ-R symptoms. Both subscales showed reversed threshold ordering and were consequently collapsed into five and four response categories, respectively. The resulting subscales were found to have good reliability and targeting.

Conclusion: Owing to the lack of unidimensionality in the FIQ-R, it is recommended that both clinical and research applications rely on subscale scores rather than a total score.