Validity and Reliability of the Turkish Version of the Glottal Function Index.

ABSTRACT

OBJECTIVES: A comprehensive evaluation is necessary for voice-related complaints, as it can benefit both the patient and physician in busy clinical settings. This study aimed to examine the Turkish adaptation of the Glottal Function Index (GFI-T), which can be quickly administered. STUDY DESIGNS Phase 1 methodological, phase 2 prospective cohort. METHODS: This study was conducted in two phases. Firstly, the GFI was translated into Turkish, and its content validity was examined. The GFI-T was administered to 40 participants with voice disorders (M=41.3, SD=10) in the study group and 40 participants without voice disorders (M=37.5, SD=11.3) in the control group. Then GFI-T was readministered 2weeks later. The collected data were used for structural and convergent validity [correlation with Turkish version of the Voice Handicap Index-10 (VHI-10)], internal consistency, and test-retest reliability analyses. Secondly, 24 participants with vocal nodules were recruited separately from the first phase and were randomly divided into three groups. The first group underwent lax-vox therapy+vocal hygiene, the second group underwent resonance therapy+vocal hygiene, and the third group was provided only with vocal hygiene recommendations. The discriminative ability and construct validity of the GFI-T were examined by comparing pre- and post-assessments. RESULTS: The results indicated that the content validity indexes were 0.98 in the experts and 0.99 in the participants. Confirmatory factor analysis of the scale confirmed that a single-factor structure and goodness-of-fit indices were suitable. The GFI-T correlated 0.92 with the Turkish version of the VHI-10. The internal consistency was 0.96, and the test-retest value was 0.99. Significant differences (P < 0.001) and correlations with the Turkish version of VHI-10 were found in intragroup comparisons. CONCLUSIONS: The GFI-T is a reliable and valid tool for the self-assessment of voice disorders. The adaptation of this study to the pediatric population is recommended.