Cross-Cultural Adaptation and Validation of Vocal Fatigue Index to the Azerbaijani-Turkish

There is no Azerbaijani-Turkish scale for assessing vocal fatigue. This study aimed to adapt the Vocal Fatigue Index (VFI) to Azerbaijani-Turkish and evaluate its validity and reliability through cross-cultural adaptation.

A cross-sectional and prospective validation design was adopted.

The VFI was translated and culturally adapted into the Azerbaijani-Turkish language according to the standard methodology of forward-backward translation. The study included 140 participants, with 70 having voice complaints and 70 not having voice complaints. Content validity was conducted with five experts through content validity index. Face validity and the pilot study were performed with 20 voice patients through cognitive interviewing. Construct validity was obtained by comparing the subtotal scores with and without vocal complaint groups. The criterion validity was calculated by comparing the correlation of the total score of the Azerbaijani-Turkish version of VFI (AT-VFI) with the Azerbaijani-Turkish version of the voice-related quality of life (AT-VRQOL) results. The discriminant validity was conducted by evaluating the area under the curve (AUC), sensitivity, specificity, and cutoff points. The internal consistency of AT-VFI was examined using Cronbach's alpha coefficient. To calculate the test-retest reliability coefficient, the AT-VFI was completed twice by 30 participants, including 20 with vocal complaint disorders and 10 without vocal complaints, at intervals of 2 weeks.

Differences in the AT-VFI scores between participants with and without voice complaints were statistically significant (P < 0.001). The construct validity results showed significant differences in the scores between the two groups in factors 1 and 2 scores (P < 0.001). The criterion validity results showed that the total score of AT-VFI with the AT-VRQOL results is correlated (r = 0.88, P < 0.001). The AUC value from the receiver operating characteristic curve was 100. The optimal cutoff point was 25.5, with a sensitivity of 100% and a specificity of 100%. The AT-VFI had high internal consistency, indicating excellent reliability (Cronbach's alpha coefficient = 0.98). The total AT-VFI scores obtained from the two administrations of the test-retest reliability were examined. It was found that there was a high degree of correlation between the scores obtained in the two administrations (r = 0.98, P < 0.001).

The AT-VFI is a valid, reliable, and sensitive index that can assess patients with vocal fatigue in the Azerbaijani-Turkish population.