Discussion
In this study, the TFI has been translated into Spanish and validated for clinical practice. To the best of our knowledge, this is the first study designed to perform a translation from English to Spanish, cross-cultural adaptation and validation of the TFI for use in Spain.
Given the psychological impact of tinnitus and the extent to which it may impair patients’ quality of life, validated disease-specific questionnaires are essential for the comprehensive assessment of this population. As we have mentioned previously, the TFI, developed by Meikle et al. in 2012, provides a reliable and valid measurement of the multiple domains of tinnitus severity and intervention outcomes.[5] The scientific literature describes other questionnaires such as the THI and VAS that may be used to assess the emotional and functional impact or loudness of tinnitus.[22] Nonetheless, the TFI has some major advantages such as its comprehensive coverage of many important tinnitus-related complaints, as well as the sum of its subscale scores providing a reliable categorization of tinnitus severity and allowing assessment of responsiveness to treatment.[9] To date, TFI has been translated, adapted and validated versions in numerous languages, including German, English, Swedish, Italian, and Mandarin Chinese.[8,9,10,23,24]
The present study found the Sp-TFI had a high overall internal consistency (Cronbach’s α of 0.83), lower than that of the original version (α of 0.97), and the aforementioned Chinese (α of 0.969), Swedish (α of 0.93) and Italian (α between 0.92 and 0.96) versions, but higher than that found in the UK (α of 0.80). Analyzing subscales separately, we found a relatively low internal consistency in the Intrusiveness and Auditory subscales (0.68 and 0.65, respectively). Given that both values are near the threshold considered to indicate acceptable internal consistency (0.7) and the moderate sample size, we might attribute these lower values to the mood of patients on the day the questionnaire was completed. Indeed, low internal consistency was not observed in the Swedish version,[10] but the UK analysis of the English version found an even lower value for Intrusiveness (α of 0.58).[9] Hence, we consider that further research should be carried out to explore the properties of the Intrusiveness subscale.
The temporal stability of the measurements was assessed using the ICC(2,1). Considering the 95% confidence interval of the ICC estimate, values greater than 0.90 are indicative of excellent reliability. Notably, we found an ICC(2,1) of 1 (CI: 0.99 – 1), indicating great test-retest reliability, even higher than values found for the original version (ICC = 0.78), for the German version (ICC = 0.91), for the Swedish version (ICC = 0.93) ).[5,8,10] and in the UK analysis of the original version (ICC = 0.91).[9] The reason for this could be that we allowed only 2 weeks between the test and retest, while Meikle et al. waited 3 months, though similarly short intervals were used to assess the other translations (between 1 and 3 weeks). Analyzing the subscales of the Sp-TFI, all the scores also had excellent reliability.
The Sp-TFI’s convergent validity with the THI was high (r=0.71, p < 0.01) and comparable to that found for the Chinese, Swedish, and Italian versions and UK analysis of the English version (r=0.86, 0.8, 0.77 and 0.75, respectively).
The evaluation of each predictive variable showed direct correlations of the THI with sex, PTA, Sp-TFI overall score, and Sp-TFI SL and R subscale scores. Meanwhile, an indirect correlation was found between the THI and Sp-TFI A subscale scores. Notably, the Sp-TFI A subscale obtained a low Cronbach’s α (α=0.65), while in analysis of the Swedish and Italian versions, the authors also observed a weaker correlation for this Auditory subscale than the other seven subscales (r=0.52 and α=0.35, respectively).
The main strength of this study is that the translation, cross-cultural adaptation, and validation of the Sp-TFI was carried out following the highest standards for translation of self-assessment questionnaires.[12] Strong validity was achieved with internal consistency higher than 0.8, comparable to results obtained for the original English and translated versions.
The main limitation of the study is that most of the authors and translators involved in this work were Spanish. For this reason, we believe that further research is necessary to assess whether linguistic and/or cultural modifications are required to adapt it for use in other Spanish-speaking countries. Moreover, despite the good results, the small sample size could lead to bias and may limit the reliability and validity of the results. Therefore, a larger sample should be recruited and used for further validation. Finally, our study suggests that the Sp-TFI is a suitable instrument for measuring the impact of tinnitus among Spanish speakers in Spain. The reliability and validity of this version seem to be very good and comparable to the original version of the TFI and indicate it can be used to assess tinnitus in clinical practice.