Validity and reliability of the glottal function index

OBJECTIVE: To evaluate a symptom-focused vocal impairment instrument for the evaluation of patients with voice disorders. DESIGN: Prospective, nonrandomized study of patients with voice disorders undergoing treatment with validation of a new symptom index, the Glottal Function Index (GFI). SETTING: Voice disorders clinic at an academic tertiary care hospital. PATIENTS: Consecutive patients undergoing therapy for glottal insufficiency, adductor spasmodic dysphonia, nodules, and granuloma (40 patients in each group) and 40 control patients. INTERVENTIONS: The Pearson correlation coefficient was used to evaluate GFI reproducibility and to compare it with the Voice Handicap Index (VHI). The paired-samples t test was used to compare pretherapy and posttherapy GFI values. MAIN OUTCOME MEASURES: Correlation of GFI with VHI; comparison of the GFI in normals, and in pretherapy and posttherapy GFI and VHI scores. RESULTS: The mean +/- SD normative GFI score was 0.87 +/- 1.32. The correlation coefficient for GFI between independent pretherapy measurements was 0.56 (P<.001). The correlation coefficient between total GFI and total VHI scores was 0.61 (P<.001). The mean posttherapy GFI scores improved among all groups as follows: glottal insufficiency: presenting GFI score, 12.7 +/- 4.1; posttherapy GFI score, 6.8 +/- 5.4; nodules: presenting GFI score, 12.9 +/- 4.2; posttherapy GFI score, 8.9 +/- 4.6; adductor spasmodic dysphonia: presenting GFI score, 13.2 +/- 4.1; posttherapy GFI score, 8.9 +/- 4.9; and granuloma: presenting GFI score, 7.8 +/- 4.6; posttherapy GFI score, 3.8 +/- 2.1. Relative to controls, the GFI score at presentation was significantly elevated and demonstrated significant reduction following treatment across each of these entities (P<.05). CONCLUSIONS: The GFI is a reliable, reproducible, 4-item, self-administered symptom index with excellent criterion-based and construct validity. Its advantages over existing indexes include brevity and ease of administration. The GFI is a useful adjunct in the evaluation and treatment of patients with glottal dysfunction.