Burnout measurement in Swiss bus drivers: a multimethod, multilingual validation of the 12-item Burnout Assessment Tool in the TRAPHEAC cohort

Introduction This study aimed to assess the psychometric validity of the 12-item Burnout Assessment Tool (BAT-12) among bus drivers - a high-risk but understudied occupational group - across the three main linguistic regions of Switzerland (German, French, and Italian). Methods The study sample comprised 494 bus drivers who completed the BAT-12 in the Transport Personnel Health Cohort (TRAPHEAC) study. Content validity was assessed by expert ratings and user interviews in French. Structural validity was examined using CFA, and cross-cultural validity through differential item functioning (DIF) analyses. Construct validity was evaluated through convergent, divergent, and discriminative analyses based on pre-defined hypotheses. Results Both the correlated four-factor and second-order four-factor CFA models showed satisfactory fit, supporting the multidimensional structure of the BAT-12. For the French version, 9 of the 12 items met the prespecified item-level content validity threshold, while the scale-level S-CVI/Ave was 0.861, approaching but not attaining the 0.90 value recommended for excellent content validity. Ordinal logistic regression identified uniform DIF for items 2 and 7 in the German-French comparison and for items 2 and 12 in the German–Italian comparison; non-uniform DIF was detected for item 8 in the German-Italian comparison. Sensitivity analyses indicated that excluding DIF-flagged items had little impact on the overall between-language comparisons. Most construct-validity hypotheses were supported, although the association between the BAT-12 and the BDI-II was stronger than expected. Discriminative validity analyses showed higher BAT-12 scores among groups expected to be at greater risk of burnout. Conclusion In Swiss bus drivers, the BAT-12 showed good structural and construct validity. Cross-language content comparability requires further investigation.