SLTinfo logo

S/Z Ratio Below 1.0

Someone writes…

“Could you please tell me what an s/z ratio below 1.0 indicates? I have not been able to find any literature explaining such a scenario.”

My reply…

Thank you for getting in touch with your question about s/z ratios.

You may wish to widen your search for clinical studies in which researchers report instances of s/z ratio below 1.0 – there are actually several studies in the literature. For example, the following two studies from 2006 and 2012 report such instances.

Marylou Pausewang Gelfer and John F. Pazera ‘Maximum Duration of Sustained /s/ and /z/ and the s/z Ratio With Controlled Intensity’ Journal of Voice, Vol. 20, No. 3, 2006.

The authors refer to several instances of s/z ratios below 1.0, e.g. “…a review of the literature on s/z ratio confirms that there is considerable overlap in the s/z ratios of those with and without laryngeal pathology. For example, in children with normal larynges, Tait et al (1) found s/z ratios of 0.67–0.92… Rastatter and Hyman (2) studied children with laryngeal pathologies and found s/z ratios of 0.81–0.93. Neither their male nor their female subjects showed the expected reduction in /z/ prolongation as a result of nodules. In a similar vein, Hufnagel and Hufnagel (3) found s/z ratios of 0.84 for male children with vocal nodules and of 1.03 in females with vocal nodules. Although the 1.03 figure may be suggestive that children with s/z ratios over one may be at risk for nodules, it should also be acknowledged that Larson et al (4) found s/z ratios of 0.90–1.12 in children with health larynges, whereas Fendler and Shearer (5) found s/z ratios of 1.13–1.42 in a similar healthy group.” (pp.370-371)


  1. Tait NA, Michel JF, Carpenter MA. Maximum duration of sustained /s/ and /z/ in children. J Speech Hear Disord. 1980; 45:239–246.
  2. Rastatter MP, Hyman M. Maximum phoneme duration of /s/ and /z/ by children with vocal nodules. Lang Speech Hear Serv Schools. 1982; 13:197–199.
  3. Hufnagle J, Hufnagle KK. S/z ratio in dysphonic children with and without vocal cord nodules. Lang Speech Hear Serv Schools. 1988; 19:418–422.
  4. Larson GW, Mueller PB, Summers PA. Effects of procedural variations in determining the s/z ratio of young children. Bulletin. J Brit Coll Speech Therapists. 1990; 863:7–8.
  5. Fendler M, Shearer WM. Reliability of s/z ratio in normal children’s voices. Lang Speech Hear Serv Schools. 1988; 19:2–4.

Mendes Tavares EL, Brasolotto AG, Rodrigues SA, Benito Pessin AB, Garcia Martins RH.’ Maximum phonation time and s/z ratio in a large child cohort’ Journal of Voice, Vol. 26, No. 5, 2012.

The authors state, “The s/z ratio was near 1.0 in most children but above 1.2 in 133 children and below 0.8 in 133 children” (p.675) and they conclude that, “These values of…s/z ratio can be used as normative…”

So, what might you make of this? If you access further studies such as these, then you will be able to frame your own opinion of what an s/z ratio of below 1.0 might indicate. You’ll see from the brief extracts above that such instances may indeed be “normative” in that there is “considerable overlap in the s/z ratios of those with and without laryngeal pathology.” Remember that the s/z ratio is a ‘rough and ready tool’. It’s quick and easy to administer but it should be considered in the context of several other assessment instruments (whether laryngoscopic, perceptual, instrumental, etc).

Good luck!