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.