Cross-Validation and Normative Values for the German Vocal Tract Discomfort Scale

Abstract

Purpose The Vocal Tract Discomfort Scale (VTD Scale) is a self-rating questionnaire investigating physical symptoms in the larynx associated with vocal pathology. The aim of this work was to investigate the reliability, validity, sensitivity, and specificity of the first German version and to provide normative data with thresholds for pathology and a scaling scheme. Study Design A retrospective multicenter study was performed. Method A total of 571 participants (409 female and 162 male), with a mean age of 47.2 years, were recruited at three German centers; of these, there were 447 participants with voice disorder and 124 vocally healthy participants. The clinical examination consisted of patient history, visual laryngeal examination, acoustic and aerodynamic assessment, perceptual analysis by the Grading-Roughness-Breathiness-Asthenia-Strain Scale, and subjective evaluation using the VTD Scale and the Voice Handicap Index (VHI). Statistics included group comparisons ( t test and analysis of variance), Pearson correlation coefficient (between VTD Scale and VHI), and Cronbach's alpha to assess validity and reliability. Analysis of receiver operating characteristics was performed to examine VTD Scale's discriminatory ability and provide a cutoff score. Additionally, percentiles were applied to provide VTD Scale ranges. Results There were highly significant differences between healthy participants and participants with voice disorder regarding the total score and both subscales of the VTD Scale. Internal consistency was excellent (α = .928). We found moderate, positive correlation between the VTD Scale and VHI (ρ = .596, p < .001). Receiver operating characteristics analysis showed an area under the curve of 0.876 ( p < .001, 95% confidence interval [0.846, 0.906]). VTD Scale ranges were no (score: 0–13), mild (score: 14–26), moderate (score: 27–40), and severe (score: 41–96) disorder. Conclusions Results confirm an excellent reliability and validity of the German VTD Scale. It provides additional and independent diagnostic information and is a useful instrument to complement voice assessment. The scaling into four severity subgroups allows the tool to be used for screening patients and considers a transferral to a voice specialist.