Cross-Cultural Adaptation and Psychometric Validation of the Serbian Version of the Back Beliefs Questionnaire in Patients with Chronic Low Back Pain

Background and Objectives: The Back Beliefs Questionnaire (BBQ) is a patient-reported outcome measure used to assess beliefs about back pain. This study aimed to cross-culturally adapt the BBQ into Serbian and evaluate the psychometric properties of the Serbian version (BBQ-Srb) in patients with chronic low back pain. Materials and Methods: A cross-sectional study involving cross-cultural adaptation and psychometric validation was conducted in 143 patients with chronic low back pain. The adaptation process included forward and backward translation, expert review, and pilot testing. Psychometric evaluation included assessment of floor and ceiling effects, internal consistency, test–retest reliability, measurement error, exploratory and confirmatory factor analyses, and construct validity testing using predefined hypotheses. Construct validity was examined through associations between BBQ-Srb scores and pain intensity, disability, pain catastrophizing, and work absenteeism. Results: The BBQ-Srb showed acceptable internal consistency, with Cronbach’s alpha of 0.728 and McDonald’s omega of 0.735. Total-score analyses were based on the preliminary exploratory 8-item BBQ-Srb version excluding BBQ13, whereas floor and ceiling effects were examined for the original 9-item scored BBQ-Srb version. Test–retest reliability was excellent (ICC = 0.916). Exploratory factor analysis suggested a predominantly one-factor structure, but the explained variance was modest. Confirmatory factor analysis of the 8-item version provided only partial support for unidimensionality, with marginal model fit and a low average variance extracted. The 8-item BBQ-Srb total score showed significant negative correlations with pain intensity, disability, and pain catastrophizing, confirming three of four predefined hypotheses. Conclusions: The BBQ-Srb demonstrated acceptable reliability and preliminary evidence of construct validity as a Serbian patient-reported outcome measure for assessing beliefs about back pain. However, structural validity was only partially supported, and the exploratory 8-item structure requires confirmation in larger, independent, and more diverse Serbian-speaking samples.