Adaptation and validation of the Rheumatoid Arthritis Quality of Life (RAQoL) questionnaire for use in Bulgaria.

Rheumatoid arthritis (RA) is a chronic disease with an enormous impact on patients' quality of life. The Rheumatoid Arthritis Quality of Life (RAQoL) questionnaire is a disease-specific measure of QoL for individuals with rheumatoid arthritis. Our aim was to adapt and validate the RAQoL for use in Bulgaria. The development of a new language version of the RAQoL consisted of three stages: translation, field testing and psychometric evaluation. The dual-panel methodology, requiring two independent panels of Bulgarian speakers, was applied to translate the UK English version of the RAQoL into Bulgarian. Face and content validity of the translated questionnaire were assessed through cognitive debriefing interviews. Lastly, the RAQoL was administered on two occasions to a random sample of RA patients to evaluate reliability and validity. At the first occasion, the SF-36 was also administered for use as a comparator scale. The RAQoL was successfully adapted into Bulgarian and considered easy to understand, acceptable and comprehensive by RA patients. A psychometric study demonstrated that the new language version has excellent internal consistency (Cronbach's alpha coefficients = 0.93 and 0.94) and test-retest reliability (a Spearman's rank correlation coefficient = 0.97). Convergent validity was established by correlating scores on the RAQoL with a comparator measure, the SF-36. A strong correlation between RAQoL scores and the physical functioning section of the SF-36 was observed. Known group validity was established by the ability of the measure to distinguish between subgroups of patients, who differed according to their perceived general health, disease severity (p < 0.001) and whether they were experiencing a flare-up (p < 0.01). The new language version is recommended for use in future research studies, clinical trials and routine practice with Bulgarian RA patients.