The S/Z Ratio as a Clinical Voice Evaluation Tool: Results of Five Experiments

Article type: Research Article

Authors: Mueller, Peter

Affiliations: School of Speech Pathology & Audiology, Kent State University, Kent, USA

Abstract: The purpose of this paper is to present data on the variability of the s/z ratio and the maximum durations from which it is derived. Productions of sustained /s/ and /z/ phonemes were collected from young children, young adults, and elderly adults, and the s/z ratios were calculated. Results of this study support the contention that subject variability for these measures is large, although not consistently of statistical significance. The results suggest that neither order nor number of trial tasks had any effect on the outcome of the s/z ratio. This suggests that clinicians could take only one measure of the /s/ and /z/ and save repeated-measure time. Furthermore, this paper basically validates the administrative procedures and interpretation guidelines of the s/z ratio as previously presented in other studies (Boone 1977; Tait, Michel, and Carpenter 1980; Eckel and Boone 1981). Nevertheless, in order to decide the usefulness of the s/z ratio’s role in the voice evaluation process, two very crucial points need to be investigated. First, a large amount of normal data from various age groups must be generated and compared to data obtained from vocally abnormal populations. Second, and perhaps most important, the aeromechanical reasons as to why the ideal s/z quotient is usually found to be near 1.0 must be addressed. Presently, this value is based on the assumption that the overall airway configuration and resistance for /s/ and /z/ are equivalent, resulting in basically identical driving pressures and flows during the production of these phonemes. Vocal tract configuration studies and aerodynamic assessments are needed to either support or reject the theoretical basis for this procedure.

Keywords: s/z ratio, voice assessment

DOI: 10.3233/ACS-1992-2108

Journal: Journal of Clinical Speech and Language Studies, vol. 2, no. 1, pp. 70-79, 1992