Friday, March 12, 2010

The One Percent Challenge

There have been many proposals for the cause and nature of stuttering. From thick tongues to parental misdiagnosis and brain mis-wiring, the history of the topic is littered with a long list of hypothesis, from the ridiculous to the reasonable. Too often in the past, these proposals were made with little knowledge of the condition, and supported without any effort to test them against observations.

There are certain observations that are repeated throughout the stuttering literature. Stutterers are fluent when speaking in unison with others, anxiety triggers stuttered speech, many children recover from stuttering at an early age, etc. Any hypothesis proposed to explain stuttering needs to account for these, and other observations - the hypothesis cannot conflict with the facts as we know them.

Of the most significant facts of stuttering is that approximately five percent of children go through a period of stuttering, and approximately one percent continue to stutter through their lives. Any proposed cause or explanation must be consistent with these numbers.

We can start by asking whether the numbers are correct. Over the last 100 years, there have been many estimates of stuttering prevalence. Although it was once claimed that some cultures did no have stutterers or words for stuttering, it is now believed that every culture in the world knows stuttering has has stuttering members.

Beyond the existence of stuttering, we could question the one percent prevalence of stuttering adults. While good numbers are not available for every tribe, clan and ethnic group, we can still say something about the prevalence of stuttering is such populations. There is no group in the world in which the prevalence of stuttering is thirty percent. In other words, there is no population in which stuttering is absent, and none is which stuttering is dramatically higher than one percent. We can say with reasonable confidence that if there was a culture in which stuttering was much more common than one percent, we would probably know about it.

So let's take the one percent estimate, and use it as a first approximation test of stuttering hypothesis. Early in the twentieth century, the influence of Freud was strong, and psychoanalytic theory was used to propose that stuttering resulted from oral-sadistic tendencies (whatever that means). We can ask, if it is true that such tendencies develop during early childhood, is it plausible that they occur in one percent of children across dramatically different cultures on different continents? Does that pass the sniff test? Different religions, different family structures and different child-rearing practices would all have to produce this same condition at the same rate. It's hard to imagine that even the confirmed Freudian of the 1920s would actually maintain such a belief when confronted.

We can ask the same question of any behavior-based hypothesis. Whatever causes the behavior - parental disapproval of normal disfluency, mistaken self-judgement of speech competence, etc, Is it plausible that this very specific speech disorder could be produced at the same rate throughout the many different cultures of the world by these methods? If the origin of stuttering were based entirely on environmental causes, why would different environments not produce different results? Do high-income parents in the United States raise more (or fewer) stutterers than working poor parents? Do rural residents produce more stutterers than urban parents? Church-going versus non-believers? Jews versus Baptists? As far as I know, the answer to all these questions is no.

Stuttering has a long history of being the square peg that is pounded into the latest and most fashionable round hole. The rise of Freudian psychology made stuttering the result of a neurosis. Learning theory made stuttering the result of classical, and then operant conditioning. In each case, true believers of new schools of psychology looked at human behavior - including stuttering - through the tinted lenses of of their belief. In a sense, each school of psychology is an ideology. That is, they follow the logic of a single idea. The more aspects of the human condition that can be explained by the theory, the grander it becomes. In many, if not all cases, those taken by the logic of a particular psychological idea seem to have staked a claim to stuttering as their own, without first testing whether their theory was consistant with the knows observations of the condition. If they had done so, decades of wasted effort could have been saved.

Knowing that across cultures, social conditions, place and time, one percent of children become persistent stutterers, it is inconceivable to me that the cause of stuttering could be found in something as variable as parental - or child's own - attitudes. As phrased above, it just doesn't pass the sniff test. In science - indeed, in rational thought - we accept that which is provisionally most likely, and reject what which runs afoul of what we hold certain. With stuttering, this fundamental principle has not been followed. Favored theories have been proposed in sequence, without regard to what are sometimes called "the facts on the ground." Entire careers - and the careers of student/followers - have been built on foundations fatally flawed. The fact that so few people have pointed out these obvious flaws is an indictment of the field as a whole.


  1. Hi Mark,

    Do you have information for any correlation between stutter rates and speaking rates in different languages and countries? For example it is well-known that in Spain people speak faster than in Sweden. Also there is clear difference in speaking rates in New Zealand and the USA for example. But slower speaking rates do not seem to (significantly) contribute to more recovered kids, even if it is widely believed that speaking more slowly reduces stuttering?..

  2. Koki

    I haven't seen any correlation between speaking rate and stuttering incidence in the literature. Speaking slowly has been part of stuttering treatment back at least to the nineteenth century, but the rate used has traditionally been much slower than any culture normally uses. Typically, stutterers have been taught to stretch out vowels, so the words themselves last longer. Of course it can work, but you've traded one unnatural form of speech for another.