Short-term and long-term test-retest reliability of the Nasality Severity Index 2.0

• Test-retest measurements of the NSI 2.0 can be performed reliably.
• No significant difference in reliability of NSI 2.0 between adults and children.
• Difference of 2.82 between two NSI 2.0 scores represents genuine change in adults.
• Difference of 2.67 between two NSI 2.0 scores represents genuine change in children.
• NSI 2.0 can be reliably applied for follow-up of hypernasality in clinical practice.

PurposeThe Nasality Severity Index 2.0 (NSI 2.0) forms a new, multiparametric approach in the assessment of hypernasality. To enable clinical implementation of this index, the short- and long-term test-retest reliability of this index was explored.MethodsIn 40 normal-speaking adults (mean age 32y, SD 11, 18–56y) and 29 normal-speaking children (mean age 8y, SD 2, 4–12y), the acoustic parameters included in the NSI 2.0 (i.e. nasalance of the vowel /u/ and an oral text, and the voice low tone to high tone ratio (VLHR) of the vowel /i/) were obtained twice at the same test moment and during a second assessment two weeks later. After determination of the NSI 2.0, a comprehensive set of statistical measures was applied to determine its reliability.ResultsLong-term variability of the NSI 2.0 and its parameters was slightly higher compared to the short-term variability, both in adults and in children. Overall, a difference of 2.82 for adults and 2.68 for children between the results of two consecutive measurements can be interpreted as a genuine change. With an ICC of 0.84 in adults and 0.77 in children, the NSI 2.0 additionally shows an excellent relative consistency. No statistically significant difference was withheld in the reliability of test-retest measurements between adults and children.ConclusionReliable test-retest measurements of the NSI 2.0 can be performed. Consequently, the NSI 2.0 can be applied in clinical practice, in which successive NSI 2.0 scores can be reliably compared and interpreted.Learning outcomesThe reader will be able to describe and discuss both the short-term and long-term test-retest reliability of the Nasality Severity Index 2.0, a new multiparametric approach to hypernasality, and its parameters. Based on this information, the NSI 2.0 can be applied in clinical practice, in which successive NSI 2.0 scores, e.g. before and after surgery or speech therapy, can be compared and interpreted.