More than 1.5 billion people around the world experience hearing loss, of whom at least 430 million experience disabling hearing loss that will require rehabilitation. The majority of people have mild to moderate hearing loss and can benefit from hearing aids. However, hearing aid adoption around the world has been low, with global hearing aid coverage being less than 11%. This is partly due to limited access to hearing healthcare services and the high cost of hearing devices.

However, there have been significant efforts to improve access to hearing healthcare services. This includes rapid advances in hearing aids and new service-delivery models leading to more affordable and accessible options such as Over-the-Counter (OTC) hearing aids. On the 17th of October 2022, the Food and Drug Administration (FDA) established a regulatory category for OTC hearing aids. The final rule allows consumers with perceived mild to moderate hearing impairment to purchase hearing aids directly from stores or online retailers without the need for a medical exam, prescription or a fitting by an audiologist. The FDA defined two sub-categories for OTC hearing aids, namely 1) OTC hearing aids with standardized output profiles (i.e., pre-set programs) and 2) self-fitting OTC hearing aids which allow users to program their hearing aids with a self-fitting strategy and also customize their hearing aid settings according to their needs and preferences.

Sabin et al. (2020) was the first study to validate a self-fitting method using the Bose prototype hearing aid. This self-fitting method allowed users to select their own signal processing parameters using a mobile application consisting of two wheels that simultaneously control the gain and compression of all frequency bands. Sabin et al. (2020) evaluated the real-world performance of this approach by comparing gain, sound quality and clinical measures of hearing aid benefit and satisfaction between a group using the self-fitting method and a group that was professionally fitted with the same hearing aid. The gain selected by the self-fit group was within 1.8 dB overall and 5.6 dB per band compared to the gain selected by the audiologist. Participants in the self-fit group reported better sound quality, and there were no differences in clinical measures of hearing aid benefit or satisfaction.

Although a number of studies have compared self-fitting OTC devices to conventional hearing aids fitted by hearing healthcare professionals, no study has compared different self-fitting strategies in the same OTC device. Therefore, this study aims to compare the existing self-fitting strategy of the Lexie Powered by Bose hearing aids (i.e., direct adjustment) to a recently validated in-situ audiometry fitting strategy. The in-situ audiometry fitting strategy consists of in-situ thresholds measurements conducted at 500, 1000, 2000 and 4000 Hz through the hearing aids, which will be used with a proprietary fitting algorithm that is based on National Acoustics Laboratories' Non-Linear Version 2 (NAL-NL2) to self-program the hearing aids.

• Objective: To compare an in-situ audiometry self-fitting strategy to the Bose self-fitting strategy (i.e., direct adjustment) using the same Lexie B2 Powered by Bose hearing aids. Hearing aid benefit and satisfaction will be compared in the same participants between the two fitting strategies. Additionally, Real Ear Measurements (REM) and speech perception will be compared in the same participants between the two fitting strategies.
• Hypothesis: The investigators hypothesize that there will be no statistically significant difference in terms of perceived hearing aid benefit and satisfaction, REM and speech perception within the same individual after receiving intervention A (hearing aid self-fitting with direct adjustment) and intervention B (hearing aid self-fitting with in-situ fitting) in a randomized, double-blind, cross-over within-subjects controlled trial.
• Design: Randomized, double-blind, cross-over within-subject controlled trial comparing an in-situ audiometry self-fitting strategy to the Bose self-fitting strategy (i.e., direct adjustment) using the same Lexie B2 Powered by Bose hearing aids in the same participants, which allows for participants to be their own control (n=40).
• Setting: This study will involve clinical audiometric testing at the Department of Speech-Language Pathology and Audiology, University of Pretoria, as well as a user field trial of the fitted hearing aids using each fitting strategy.
• Participants: Eligible participants will include 40 adults (>18 years) with a self-perceived mild-to-moderate level of hearing loss, without symptoms of outer- and middle ear pathology and who own a smartphone with access to mobile data (Android or iOS). Participants will be recruited and will randomly be assigned to a group using computer-generated randomization by an independent research assistant after being stratified for sex and degree of hearing loss.
• Intervention: Forty participants will randomly be assigned to be fitted with intervention A (hearing aid self-fitting with direct adjustment) or intervention B (hearing aid self-fitting with in-situ fitting) and wear the hearing aids for four weeks. After four weeks, they will be crossed over to be fitted with the alternative fitting strategy, and they will wear the hearing aids again for four weeks.
• Outcome measures: The primary outcome measure will be the Abbreviated Profile of Hearing Aid Benefit (APHAB). The secondary outcome measures will be the International Outcome Inventory for Hearing Aids (IOI-HA), Overall experience rating, REM, the QuickSIN speech-in-noise test and the Digits-in-noise test.

Inclusion criteria:

1. Adults (>18 years) living in South Africa
2. Good English proficiency (measured using an online English proficiency test as well as self-report of English speaking competence)
3. Must have mild-to-moderate self-perceived hearing difficulties
4. Possession of a smartphone compatible with the Lexie app (iOS or Android)
5. Access to mobile data to operate the Lexie app
6. Must have transport to visit the initial and follow-up assessments

Exclusion criteria:

1. Normal hearing or self-perceived severe-to-profound hearing loss
2. Active outer or middle ear pathology
3. Poor English proficiency
4. Diagnosed cognitive impairment