The use of a prescriptive fitting approach for hearing aid selection has been a common
practice for the past 60–70 years. While there are prescriptive approaches that have
been validated, in recent years it has become popular to deviate from these validated
methods and use manufacturers' proprietary algorithms, which in many cases are significantly
different. This research review was designed to examine if there was evidence supporting
the use of specific gain requirements for hearing aid fitting. Specifically, the question
that was asked was "Are there real-world outcome measures from adult patients that
show a preference for the gain prescribed by a specific prescriptive fitting procedure?"
Inclusion criteria were as follows: adult subjects, consistent technology (e.g., different
prescriptive methods compared using same hearing aids), real-ear verification of gain,
and real-world outcome measures. For this review, in addition to subjective responses,
preferred use gain was considered a real-world outcome measure. The National Acoustic
Laboratories' revised (NAL-R), revised for severe/profound (NAL-RP), and the National
Acoustic Laboratories—Non-Linear 1 (NAL-NL1) prescriptive methods were used as a common
reference, as they have been the most commonly studied methods with adults.
Eleven studies were identified that met the inclusion criteria. Eight of the studies
supported gain similar to that prescribed by the NAL-R or NAL-RP methods; three studies
supported prescribed gain less than the NAL-R or NAL-RP. There was no evidence that
gain greater than that prescribed by the NAL methods should be used. The level of
evidence was moderate, as the supporting studies were either Level 2 or Level 4, and
the statistical power of the studies was low.
Key Words
Evidence - formula - gain - hearing aid - NAL - outcome - prescription - real world
