The effect of using time intervals of different length on judgements about stuttering

Conventional clinical procedures for assessment of stuttering are reported to have poor reliability. Time interval analysis procedures have been reported to produce greater reliability than the conventional procedures. In time interval procedures, successive intervals of the same duration are extracted from a sample of speech and judged by participants as stuttered or fluent. There is a problem insofar as the amount of speech judged stuttered depends on the length of the interval used. This problem is illustrated in an experiment in which 1-s and 5-s intervals were drawn from the same samples of speech and judged by participants as stuttered or fluent. It is also shown that the problem of lack of sensitivity when longer intervals are used is more acute for individuals who exhibit severe stuttering. Since ability to detect changes in stuttering rate is dependent on the length of interval used (as well as stuttering severity), the procedure can highlight or disguise changes in stuttering rate depending on parameterization of interval length and choice of participants to study. Thus, use of different length intervals across studies can distort whether particular treatments have an effect on speech control. Therefore, it is concluded that time interval analysis, as it is currently used, is an unsatisfactory procedure. If a standard-length interval could be agreed, comparison across studies or analyses would be possible.