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.