The authors utilized the Stuttering Severity Instrument (versions 3 and 4) procedures for the assessment of readers and non-readers to see whether they give equivalent scores. Older children (ages 10-0 to 14-7) provided spontaneous and read samples, which were scored for severity according to reader and non-reader procedures. The authors reported confirmation of no significant difference in severity scores for the older children when the reader and non-reader procedures were used, and confirmed 200 syllables to be the minimum for obtaining stable SSI severity scores.
Todd, Helena, Mirawdeli, Avin, Costelloe, Sarah, Cavenagh, David, Stephen, and Howell, Peter. (2014). Scores on Riley’s Stuttering Severity Instrument Versions Three and Four for samples of different length and for different types of speech material. Clinical
Linguistics & Phonetics. doi:10.3109/02699206.2014.926991