Purpose: The fourth version of the Stuttering Severity Instrument (SSI-4) has been available since 2009. It has some modifications and new features which make it more appropriate at least for clinical practice, although further documentation is needed. The objective of the current research was to translate SSI-4 into Persian language and to discuss its relative and absolute reliability as well as its criterion validity for Persian adults who stutter (PWS). We also aimed to study how the new subjective self-reports of the SSI-4 complement the stuttering severity score obtained from the SSI-3 or the SSI-4.
Method: The cross-cultural guideline recommended by the International Quality of Life Assessment project was used to translate the SSI-4 into Persian language. Thirty five PWS from ages 17 to 42 were recruited and 10 speech and language pathologists assessed their stuttering severity using either the SSI-4 or stuttering severity ratings (SR) to test validity and reliability of the Persian translated version.
Results: A very high inter-judge relative reliability along with a poor absolute inter-judge reliability was found for the SSI-4 scores. The results were more promising for the intra-judge absolute reliability. Test-retest reliability of the complementary questions to the SSI-4 was also found acceptable. However, no strong relationship was found between the SSI-4 scores and its complementary questions.
Conclusion: The Persian version of the SSI-4 can be used reliably by trained SLPs for research and clinical purposes, but not to document small changes in stuttering severity. We argue that the response of participants to the complementary self-report questions should also be considered in calculating their stuttering severity score.