Objective: The Tinnitus Handicap Inventory (THI) is widely used in clinical practice and research as a three-dimensional measure of tinnitus severity. Despite extensive use, its factor structure remains unclear. Furthermore, THI can be considered a reliable measure only if Cronbach's alpha coefficient and Classical Test Theory is used. The more modern and robust Item Response Theory (IRT) has so far not been used to psychometrically evaluate THI. In theory, IRT allows a more precise evaluation of THI's factor structure, reliability, and the quality of individual items.
Method: There were 1115 patients with tinnitus (556 women and 559 men), aged 19-84 years (M = 51.55; SD = 13.28). The dimensionality of THI was evaluated using several models of Confirmatory Factor Analysis and an Item Response Theory approach. Exploratory non-parametric Mokken scaling was applied to determine a unidimensional and robust scale. Several IRT polytomous models were used to assess the overall quality of THI.
Results: The bifactor model had the best fit (RMSEA = 0.055; CFI = 0.976; SRMR = 0.040) and revealed one strong general factor and several weak specific factors. Mokken scaling generated a reliable unidimensional scale (Loevinger's H = 0.463). In order to refine THI we propose that five items be removed. The IRT Generalized Partial Credit Model generated good parameters in terms of item location (difficulty), discrimination, and information content of items.
Conclusion: Our findings support the use of THI to evaluate tinnitus severity in terms of it being a reliable unidimensional scale. However, clinicians and researchers should rely only on its overall score, which reflects global tinnitus severity. To improve its psychometric quality, several refinements of THI are proposed.