Vocal Fatigue Index: Validation and Cut-off Values of the Brazilian Version

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Objectives: To complete the validation and to study the psychometric properties of the Brazilian Portuguese version of the Vocal Fatigue Index (IFV). Material and methods: This is a validation study of a diagnostic instrument utilizing a cross-sectional design and phases with quasi-experimental design. The total sample was composed of 212 participants, divided into two groups: Dysphonic Group and Vocally Healthy Group. All participants answered the VFI protocol. Data analysis consisted of the following steps: exploratory factor analysis, validity analysis, reliability analysis, sensitivity analysis, receiver operating characteristic, and area under the curve analysis. Results: The Brazilian Portuguese version of the VFI called Índice de Fadiga Vocal-IFV, has 17 items and four factors. The IFV is a valid, reliable and sensible instrument to measure the self-perception of vocal fatigue. The threshold values for each factor was: 4.50 for tiredness and voice impairment; 3.50 for avoidance of voice use; 1.50 for physical discomfort and 8.50 for improvement of voice symptoms with rest. The threshold value for the total score was 11.50. Conclusion: The Brazilian Portuguese version of the VFI is a valid instrument to assess the self-perception of vocal fatigue, especially in dysphonic individuals.