ABSTRACT
OBJECTIVE: To culturally adapt the Glottal Function Index (GFI) questionnaire to the Lithuanian language, and to validate it. METHODS: Psychometric analyses were performed on the translated Lithuanian version of the GFI (GFI-LT) as described by the Scientific Advisory Committee of the Medical Outcomes Trust. The GFI-LT was completed by 50 voice-disordered individuals and by 50 healthy subjects of the control group. Validity, reliability, reproducibility, sensitivity, and responsiveness to clinical change of the GFI-LT were evaluated. To assess the concurrent validity of the GFI-LT, all participants also completed the Voice Handicap Index (VHI) questionnaire. RESULTS: The GFI-LT showed a statistically significantly high reliability and internal consistency (Cronbach α=0.8, r=0.50), and moderate item-total correlation (r=0.41-0.55). Cronbach α coefficients of the test-retest reliability were above the standard (≥0.9) for individuals testing. There was a statistically significant difference between the mean scores of the control and the voice-disordered groups (P<0.001). The Receiver Operating Characteristic test indicated that the GFI-LT score of >3.0 was the optimal score distinguishing patients and healthy controls with the sensitivity of 88% and specificity of 84%. Statistically significant (P<0.05) strong correlations were found between the GFI-LT and VHI scores. The GFI-LT was found to be a responsive measurement instrument to patients' clinical statement; mean difference of the GFI-LT scores in the group of voice-disordered patients before and after surgical treatment was 5.7 (P<0.001). CONCLUSION: The GFI-LT is considered to be a valid and reliable tool for self-assessment of the severity of voice disorders in Lithuanian-speaking patients.
