Perceptual rating instrument for speech evaluation of stuttering treatment.

A rating instrument is described that can be used to assess the results of stuttering treatments. The instrument is designed for use with naive listeners. It yields a comprehensive and detailed description of the speech quality in terms of articulation, phonation, pitch, and loudness; in addition, it includes a naturalness scale. Analysis of ratings obtained with the instrument show that naturalness is a multidimensional characteristic. Moreover, the speech characteristics that determine the naturalness ratings appear to be different pretreatment, posttreatment, and at follow-up treatment. The psychometric characteristics of the instrument are analyzed in detail. It is concluded that mixing of samples of stutterers and nonstutterers in one rating experiment may artificially inflate the reliability of the ratings. Also, ratings on equal-appearing interval scales cannot be interpreted in an absolute sense. Solutions for this methodological problem are suggested.