Difference in SII provided by initial fit and NAL-NL2 and its relation to self-reported hearing aid outcomes.

Objective: The speech intelligibility index (SII) is used to quantify the audibility of the speech. This study examined the relationship between self-reported hearing aid (HA) outcomes and the difference in aided SII (SII _A ) calculated from the initial fit (IF) gain and that prescribed as per the second generation of National Acoustic Laboratory Non-Linear (NAL-NL2).
Design: A prospective observational study.
Study Sample: The study included 718 first-time and 253 experienced HA users. All users had a valid real-ear measurement (REM) at three input levels (55, 65 and 80 dB SPL).
Results: The gain provided by IF was lower than NAL-NL2 at 55 and 65 dB SPL. IF gain exhibited reduced compression than NAL-NL2 as input levels increased from 55 to 80 dB SPL. On average, the SII _A provided by IF was significantly lower than that for NAL-NL2 at all input levels. The difference in SII _A between IF and NAL-NL2 at 80 dB SPL input level with 0 dB signal-to-noise ratio (SNR) turned out to be a predictor for self-reported outcome for first-time HA users.
Conclusion: The study suggests that an SIIA close to that provided by NAL-NL2 at high input levels would be preferred to obtain a better self-reported outcome. .