The s/z Ratio and Its Implications
Chris Vaughan B.A. & Lissa Power-deFur, Ph.D., CCC-SLP
Literature Review
What is the s/z ratio?
Purpose

This describes the maximum phonation of /s/
divided by the maximum phonation of /z/ (Eckel
& Boone, 1981).

This aids in the understanding of the efficiency
of the glottis (Gelfer & Pazera, 1997), the
function of the vocal folds, the effectiveness of
voice treatments (Eckel & Boone, 1981), and is
an indicator of reduced vital capacity or poor
control over one’s respiration (Tait & Mechel et
al., 1980).
-Reach a better
understanding of the s/z
ratio.
-Compare results with
previous research.
-How does the s/z ratio
affect the responsibilities of
a Speech-Language
Pathologist?
Results
Average duration
/s/
Male
Average
(used the
highest /s/
and /z/
durations)
26.8
5
sec
Female
Average
(used the
highest /s/
and /z/
durations)
33.0
7
sec
/z/
30.
8
sec
31
sec
Longest Duration Reached
s/z
.87
1.06
Reached
Reached
longest /s/ longest /z/
duration
duration
(males and (males and
females)
females)
1st
6
5
attempt participants participants
2nd
4
10
attempt participants participants
rd
3
10
5
attempt participants participants
Men sustained /s/ and /z/ longer than women
1.0 ratio for both men and women
Longest duration at trial 7 (out of 10)
/s/ slightly longer out of 10 trials; /z/ slightly longer out
of 3 trials

Gelfer et al., 1997
As age increases, so does maximum phonation
duration
Phonation duration depends on height

Tait et al., 1980
Those with nodules and/or polyps appear to have
decreased /z/ maximum phonation duration due to
increased vocal fold mass which affects the adduction
of the vocal folds during /z/. This effect causes an
increase in air to escape the glottis.

Eckel et al., 1981
Participants
-13 females and 1 male from the
Speech Science class at Longwood
University
-2 male graduate students from
Longwood University’s CSDS program
-4 male volunteers from Richmond,
Virginia
Method
Undergraduate participants answered
a questionnaire as well as documented
phonation duration times for the
phonemes /s/ and /z/ which they had
previously documented for their
Speech Science class.
Ratio as indictor of illness
Average Average s/z
/s/
/z/
ratio
Reported to 32.8 sec 28.2 sec 1.16
be sick
and/or had
respiratory
issues (5
participants)
Reported not
feeling sick
and did not
have a
history of
respiratory
issues (15
participants)
30.26
sec
31.86
sec
Implications
Implications for Clinicians

More than 3 trials need to be administered to get a clear understanding of a client’s s/z ratio.

Gender makes a difference concerning maximum phonation duration.

Should not expect large maximum phonation durations for /s/ and /z/ with a young child.

Note when a client has a consistent s/z ratio above 1.0. This may point to laryngeal pathology.
Future Research Suggestions

More trials are needed to obtain a better understanding of the s/z ratio.

Larger number of participants.

Height should be taken into consideration during computation of the s/z ratio.

Data gathered by researcher rather than individual reports.

Equal number of males and females.

Include children and senior citizens to compare maximum phonation durations.
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Findings
This research supported findings from Gelfer’s (1997)
study which determined that the s/z ratio for women is
about 1.0. Also, when providing three trials, /z/ is
sustained the longest.
Findings supported Tait’s (1980) study which found that
as age increased, so did the maximum phonation
duration. In this study, this was found true between the
ages of 21 to 28.
This research concluded that those who reported
feeling sick or had a history of respiratory issues had
on average lower phonation durations for /z/. This was
possibly due to increased vocal fold size, excess
mucus on the vocal folds, and/or poor respiratory
support.
Limitations
-Limited number of participants: 20
-Unequal numbers of males and females in the research
group
-The Speech Science class timed their own /s/ and /z/
maximum phonation duration trials. Even though all the
participants were given the same directions, because of
this, the /s/ and /z/ phonation durations from the class may
have been affected.
-Limited number of trials: 3
-Only 4 participants knew nothing about the s/z ratio.
These 4 participants were all males; therefore this may
have skewed the male participant data.
Graduate and Richmond participants
answered a questionnaire and
completed 3 maximum phonation trials
for both /s/ and /z/. These were
computed by the researcher.
Along with gathering /s/ and /z/ data,
the questionnaire to all participants
requested the following information:
-Age
-Gender
-Do you feel sick the day of the s/z
ration study?
-If yes, does your illness affect your
respiration?
-Do you have a history of respiratory
issues?
References
Eckel, F.C., & Boone, D.R. (1981). The S/Z ratio
as an indicator of laryngeal pathology. The
Journal of Speech and Hearing Disorders,
46(2), 147-149. Retrieved from
http://search.proquest.com/docview/85151
671?accountid=12144.
Gelfer, M. P., & Pazera, J. F. (2006). Maximum
duration of sustained /s/ and /z/ and the
s/z ratio with controlled intensity. Journal
of Voice : Official Journal of the Voice
Foundation, 20(3), 369-379. Retrieved
from
http://search.proquest.com/docview/85392
865?accountid=12144.
Tait, N. A., Michel, J. F., & Carpenter, M. A. (1980).
Maximum duration of sustained /s/ and /z/
in children. The Journal of Speech and
Hearing Disorders, 45(2), 239-246.
Retrieved from
http://search.proquest.com/docview/85150
517?accountid=12144.