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Reliability and Validity of Speech Evaluation in Adductor Spasmodic Dysphonia

Abstract

Objectives. In order to establish a reliable diagnostic tool for adductor spasmodic dysphonia (ADSD), it is necessary to determine the proper terms representing its characteristic voice symptoms and to relate them to objective measures such as acoustic parameters or speech perturbation. The aim of this study was to evaluate speech in patients with ADSD by perceptual evaluations and acoustic measures, and to examine the reliability and validity of the measures by comparison with normal controls. Methods. Twenty-four patients with ADSD and 24 healthy volunteers matched to the ADSD patients with regard to age and sex participated in the study. Speech materials, consisting of three short sentences, were constructed from serial voiced syllables to elicit abductor voice breaks. Three otolaryngologists specializing in phoniatrics rated the degree of voice symptoms using a visual analog scale (VAS). VAS sheets with five 100-mm horizontal lines were given to each rater. The ends of the lines were labeled normal versus severe, and the five lines were labeled as overall severity and each of the four voice symptoms; strangulation, interruption, tremor and strained speech. Nine words were selected from the speech materials for acoustic analysis, and abnormal acoustic events were classified into one of the three categories; percentage of frequency shifts, percentage of aperiodic segments, or percentage of phonation breaks. Acoustic measures were performed by a speech-language-hearing therapist specializing in voice disorders and five healthy university students. To evaluate the intra- and inter-rater/measurer reliability of the VAS scores or acoustic measures, Pearson r correlations were calculated. To examine the validity of perceptual evaluations and acoustic measures, the sensitivity, specificity, positive predictive value and negative predictive value were calculated. Results. Pearson r correlation coefficients for overall severity showed the highest intra- and inter-rater reliability, and reliability coefficients for one of the four voice symptoms, strangulation (r = 0.816-0.937), were slightly higher than those for the other symptoms. For acoustic events, intra-measurer reliabilities were r = 0.645 (frequency shifts), r = 0.969 (aperiodic segments), and r = 1.0 (phonation breaks), and inter-measurer reliability ranged from r = 0.102 to r = 1.0 (average r = 0.861). The Pearson r correlation coefficient for phonation breaks was higher than those for the other acoustic events. Perceptual evaluation using VAS showed high sensitivity (91.7 %) and specificity (100 %), and acoustic analysis showed low sensitivity (70.8 %) and high specificity (100 %). Eight of the 24 patients were judged to be within normal limits by one or both evaluation methods. Conclusions. Both perceptual evaluation and acoustic measures alone were found to be likely to miss true ADSD patients. It is important to obtain a range of speech materials and to use a combination of perceptual evaluation and acoustic measures based on our understanding of the advantages and disadvantages of both methods

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