Adaptation and validation of the Bulgarian version of the Systemic Lupus Erythematosus Quality of Life Questionnaire (L-QoL)

Objective Systemic lupus erythematosus (SLE) is a heterogeneous disease with multiple clinical manifestations, which causes a significant deterioration in the quality of life (QoL). The Systemic Lupus Erythematosus Quality of Life Questionnaire (L-QoL) is a lupus-specific measure used to determine the burden of the disease and it applies the need-based model of QoL. Our aim was to produce the first successfully validated foreign language version of the questionnaire.Methods The development of the Bulgarian version involved three stages: translation, field testing and psychometric evaluation. Translation was conducted by an expert linguist working with a developer of the original L-QoL, followed by interviews with monolingual lay individuals. Face and content validity of the translation were assessed by cognitive debriefing interviews with Bulgarian SLE patients. Finally, the L-QoL was validated by administering the questionnaire to a random sample of SLE patients on two occasions, 2 weeks apart to evaluate its reliability and validity.Results In the validation survey, the new Bulgarian version demonstrated high internal consistency (the Cronbach's alpha coefficient was 0.92), and test-retest reliability (0.97). Additionally, scores on the L-QoL were correlated with those on the SF-36 sections to determine convergent validity and the strongest correlation was observed between L-QoL scores and the social functioning section of the SF-36. Known group validity was established by testing the ability of the Bulgarian L-QoL to distinguish between subgroups of patients from the study pool.Conclusions The demonstrated excellent psychometric properties ensure that the Bulgarian L-QoL accurately captures the impact of SLE on the quality of life.