The Vocal Tract Discomfort Scale: Validity and Reliability of the Persian Version in the Assessment of Patients With Muscle Tension Dysphonia

Abstract

To cross-culturally adapt of Persian Vocal Tract Discomfort (VTDp) scale and evaluate its validity and reliability in the assessment of patients with muscle tension dysphonia (MTD). A cross-sectional and prospective cohort design was used to psychometrically test the VTDp. The VTD scale was cross-culturally adapted into Persian language following standard forward-backward translations. The VTDp scale was administrated to 100 patients with MTD (54 men and 46 women; mean age: 38.05±10.02years) and 50 healthy volunteers (26 men and 24 women; mean age: 36.50±12.27years). Forty-five patients with MTD completed the VTDp 7days later for test-retest reliability. Patients also completed the Persian Voice Handicap Index (VHIp) to assess construct validity. The results of discriminative validity demonstrated that the VTDp was able to discriminate between patients with MTD and healthy participants. The internal consistency was confirmed with Cronbach α .77 and 0.73 for VTDp frequency and severity subscales, respectively. The test-retest reliability was excellent with an intraclass correlation coefficient (ICCagreement) of 0.93 for the frequency subscale and 0.91 for the severity subscale. Construct validity of the VTDp was shown with significant correlations between the VTDp frequency and severity subscales and the VHIp total scores (0.36 and 0.37, respectively). The standard error of measurement and smallest detectable change values for VTDp frequency (2.11 and 5.85, respectively) and severity (2.25 and 6.23, respectively) were acceptable. The Bland-Altman analysis for assessing the agreement between test and retest measurements showed no systematic bias. The VTDp is a valid and reliable self-administered scale to measure patient's vocal tract sensations in Persian-speaking population.