Aided Speech Intelligibility Index
Also written as: SII — Speech Intelligibility Index
A calculated measure estimating the proportion of the long-term average speech spectrum that is audible and usable to a hearing aid user, weighted by the importance of each frequency band for speech understanding.
Full Definition
The Speech Intelligibility Index (SII) is a standardised metric derived from ANSI S3.5 that predicts the intelligibility of speech under given acoustic conditions. When applied in audiological practice to a patient wearing hearing aids, it is referred to as the 'aided SII' and is often generated automatically within hearing aid fitting software using real-ear or simulated target data. Values range from 0 (no audible speech cues) to 1.0 (all speech cues audible), and the result is frequently expressed as a percentage. Editors should note that SII differs from earlier metrics such as the Articulation Index (AI) and that these terms are not fully interchangeable in current literature.
Usage
Usage note: Do not use the older term 'Articulation Index (AI)' in current clinical documents; the ANSI S3.5-1997 standard replaced it with SII. Spell out in full on first use and provide the acronym in parentheses.
In Context
- "The fitting software displayed an aided Speech Intelligibility Index of 0.72, indicating good audibility for average conversational speech." — Real Ear Measurement Report
- "Reviewers flagged that the author had incorrectly used 'Articulation Index' where the current standard term is 'Speech Intelligibility Index'." — Peer Review Comment