Psychometric assessment of the Japanese version of the Revised Fibromyalgia Impact Questionnaire: reliability and validity

Aim To assess the psychometric properties of the Japanese version of the Revised Fibromyalgia Impact Questionnaire (JFIQR) in fibromyalgia (FM) patients. Method The reliability and validity of the JFIQR were assessed using online data collected from Japanese FM patients. Reliability was evaluated based on test-retest reliability results and internal consistency; validity was evaluated on the basis of concurrent and known-group validity. Results A total of 105 patients completed the online questionnaire. Intra-class correlation coefficients for test-retest were 0.91 for the JFIQR total score with a range of 0.84–0.90 in three domains: function, overall impact and symptoms. Internal consistency results indicated a Cronbach's alpha of 0.90 for the total score with a range of 0.83 and 0.85 for the domains. Concurrent validity results showed that the total score was correlated to all external criteria (Japanese version of the Fibromyalgia Impact Questionnaire, Fibromyalgia Activity Scale-31, Medical Outcomes Study 36-item Short-Form health survey) from a moderate to strong degree with most indicating a strong correlation. Results of known-group validity showed that the JFIQR total score is capable of discriminating between FM and the other groups, such as rheumatic arthritis and no chronic pain (P < 0.0001 for all pairwise comparisons). Conclusion The current psychometric assessment of the JFIQR demonstrated that it is a reliable and valid questionnaire in Japanese patients with FM. Usefulness of the JFIQR in clinical studies and medical practice for Japanese-speaking populations is expected.