Cross-Cultural Adaption and Validation of the Vocal Fatigue Index in German

Objective: The purpose of the study was to implement a cross-validation and adaption of the Vocal Fatigue Index (VFI) in German language.

Methods: The translation process for the German version (GV) of the VFI passed through three steps of translation before a final version was completed. Study subjects included 100 vocally healthy subjects and 101 voice-disordered subjects with various types of dysphonia. The internal consistency was determined using Cronbach's alpha (cron α) and the item-total analysis. Test-retest reliability was measured with the Pearson correlation coefficient. To assess the validity, the independent sample t test, the receiver-operating characteristic curve, the likelihood ratios, and Youden Index were used.

Results: The internal consistency across all three domains were good (#1: cron α = 0.945, #2: cron α = 0.904, and #3: cron α = 0.871) and no item of the GV of the VFI had to be deleted for further analysis relating to the item-total analysis. The test-retest reliability was high to very high (r = 0.86-0.93). Significant higher scores were revealed in voice-disordered subjects in comparison with vocally healthy subjects in all three domains (all Pvalues <0.01). Thresholds for the three domains of the GV of the VFI were determined at ≥15.5 (76.2% sensitivity and 90.0% specificity) for #1, ≥2.5 (71.5% sensitivity and 81.0% specificity) for #2, and ≤7.5 (50.5% sensitivity and 80.0% specificity) for #3.

Conclusions: It can be considered that the VFI is a valid and reliable tool identifying vocal fatigue symptoms and its severity in the German-speaking population.