What percentage of stuttering behavior is normal?

A recent Facebook post asked what percent of disfluency was considered to be in the normal range.

Like so many questions surrounding stuttering, the answer turns out to be somewhat complicated! Historically, people have used various set values, such as 3% syllables stuttered or a 10% overall disfluency rate to indicate that a person’s speech fluency was above or below normal limits.

While these metrics may have their place, I want to highlight some of the (many) concerns with using frequency counts for identifying people who stutter and of using average numbers of disfluencies for diagnostic or treatment purposes. Most importantly, the frequency of stuttering a person exhibits doesn't necessarily tell us much about whether the person needs therapy (or even how he's doing in therapy). And, what we do with frequency information also depends a lot upon the person’s age.

For a preschool child, it is far more important to consider other factors, for research has shown that the amount of stuttering a child does doesn't really relate to whether or not the child needs therapy. A child may be well above the 2% or 3% syllables stuttered or even 10% overall figures cited above yet still not need intervention; other children may be below those numbers but still need help. The real factor in determining whether or not a preschool child needs therapy is whether or not he is at risk for continuing to stutter. If he is at risk, then therapy is indicated; if he is not, then you will probably still want to do some work to educate the parents and others about the child's fluency development, but it may not be as necessary to enroll the child in formal intervention immediately.

For a school-age child, adolescent, or adult, remember that the amount of stuttering (frequency or severity) really isn't a factor in determining whether the person needs treatment. In the schools, we are supposed to qualify children for intervention based on whether they are experiencing adverse impact as a result of the communication difficulty. For adults, the same issue holds: the need for therapy is based on impact rather than on the amount of stuttering. Some people may exhibit a lot of stuttering and have minimal adverse impact (and therefore not need intervention); others may exhibit minimal observable stuttering but need help because they are avoiding talking or changing words and not saying what they want to say. Therefore, other measures (such as the OASES for evaluating the adverse impact of stuttering) what come into place for these populations.

All of these concerns about the observable frequency of stuttering are in addition to the fact that stuttering is highly variable. Thus, the frequency count or severity rating you get in one situation isn’t necessarily the same as the frequency count you’ll get in another situation. This means that we need to collect data in multiple settings to understand the range of stuttering behaviors a person exhibits. (Even then, this doesn’t tell us about impact, but at least we’ll get a better measure of the observable features.) There are also difficulties with the reliability of measurement of stuttering behaviors. Ample literature has shown that without training, clinicians are not terribly reliable and making stuttering frequency count judgments. Fortunately, research also shows that training can help! If you find that you do need to make frequency counts, you can improve your ability to do that by taking courses on stuttering measurement. (For example, I have a course on stuttering measurement at MedBridge Education (www.MedBridgeEducation.com/scott-yaruss).

There’s so much more to be said on the topic of stuttering measurement, but the most important piece to remember is that there really is predetermined or set frequencies of stuttering or disfluency behavior really don’t tell us much about the speaker’s need for therapy or experience of stuttering. We ought to consider factors other than just the observable frequency of stuttering when determining whether a person who stutters needs therapy, making decisions about the nature of that therapy, and examining their progress in therapy.

“Stuttering is more than just stuttering,” so our assessment and treatment should examine more than just the observable speech behaviors.

J Scott Yaruss

Written by : J Scott Yaruss

J. Scott Yaruss, PhD, is a professor of Communicative Sciences and Disorders at Michigan State University. He has published more than 70 peer-reviewed manuscripts, more than 115 other papers on stuttering, and several clinical resources, including the Overall Assessment of the Speaker's Experience of Stuttering (OASES), Early Childhood Stuttering: A Practical Guide, School-Age Stuttering Therapy: A Practical Guide, the Minimizing Bullying program, and more (all published by Stuttering Therapy Resources, Inc.).