Cross-Cultural Adaptation and Validation of the Vocal Fatigue Index (VFI) to Danish.

Objectives: The aim was to cross-culturally adapt and validate the Vocal Fatigue Index (VFI) to Danish (DK-VFI).

Study design: Cross-sectional design.

Methods: The original American English VFI was cross-culturally adapted to Danish using a forward-backward translation procedure combined with focus group interviews. The DK-VFI was distributed to 26 patients with vocal fatigue (VF) and 103 vocally healthy controls. A matched subsample based on age and sex of the control group was included. Internal consistency was determined using Cronbach's alpha and test-retest reliability was determined using Spearman's Rho as well as Wilcoxon signed-rank tests. Validity was confirmed using the Wilcoxon rank-sum test. Sensitivity and specificity were assessed using the Receiver Operating Characteristics test and the discriminative ability was determined using the Area Under the Curve (AUC) test. The original VFI consists of three factors, and cutoff values were calculated for each separate factor in the DK-VFI.

Results: Minor changes were made in the phrasing of specific questions in order to appropriate the VFI to the Danish language. The internal consistency for the DK-VFI was high, with a Cronbach's alpha of α = 0.95. The results showed statistically significant differences (P < 0.05) in mean scores of the DK-VFI between patients and controls. The cutoff values between patients and controls for each separate factor were ≥11.5 for factor 1, ≥2.5 for factor 2, and ≤5.5 for factor 3. The results of the AUC analysis showed that the DK-VFI has discriminative abilities of 0.94 for factor 1, 0.92 for factor 2, and 0.82 for factor 3. Analysis of test-retest reliability showed strong reliability for the patient group and acceptable reliability for the control group.

Conclusion: The DK-VFI is a valid and reliable tool for identifying symptoms of VF and can sensitively discriminate people with VF from vocally healthy controls.