Maximum duration of sustained /s/ and /z/ in children.

It has been proposed in the clinical literature that a ratio of the maximum duration of /s/ to /z/ may be useful in determining the possible contribution of the respiratory and vocal mechanisms to a disordered voice. The purpose of this study was to obtain preliminary normative data for the maximum phoneme duration (MPD) of /s/ and /z/ and to determine the ratio of /s/ to /z/ in five, seven, and nine year olds. The results indicated that while there were no significant differences in MPD for either /s/ or /z/ between males and females at any one age level, there was a significant increase in the MPD of /s/ and /z/ for both sexes as a function of age. When the ratio of /s/ to /z/ was computed for the subjects, there were no significant differences in these ratios between males and females nor were there significant differences as a function of age.