Psychometric validity, reliability, and responsiveness of the tinnitus functional index

Background: The effects of treatments on tinnitus have been difficult to quantify. The Tinnitus Functional Index (TFI) has been proposed as a standard questionnaire for measurement of tinnitus treatment outcomes. For a questionnaire to achieve wide acceptance, its psychometric properties need to be confirmed in different populations. Objective: To determine if the TFI is a reliable and valid measure of tinnitus, and if its psychometric properties are suitable for use as an outcome measure. Research Design: A psychometric evaluation of the TFI from secondary data obtained from a crosssectional clinic survey and a clinical trial undertaken in New Zealand. Study Sample: Confirmatory factor analysis and evaluation of internal consistency reliability were undertaken on a sample of 318 patients with the primary complaint of tinnitus. In a separate sample of 40 research volunteers, test-retest reliability, convergent and divergent validity were evaluated. Both samples consisted of predominantly older Caucasian male patients with tinnitus. Results: The internal structure of the original US TFI was confirmed. The Cronbach's Alpha and Intraclass correlation coefficients were > 0.7 for the TFI overall and each of its subscales, indicating high internal consistency and test-retest reliability. Strong Pearson correlations with the Tinnitus Handicap Questionnaire and tinnitus numerical rating scales indicated excellent convergent validity, and a moderate correlation with the Hearing Handicap Inventory, indicated moderate divergent validity. Evaluation of the clinical trial showed good test-retest reliability and agreement between no-treatment baselines with a smallest detectable change of 4.8 points. Conclusions: The TFI is a reliable and valid measure of tinnitus severity in the population tested and is responsive to treatment-related change. Further research as to the TFI's responsiveness to treatment is needed across different populations.