Prescribed clinician-fit versus as-worn coupler gain in a group of elderly hearing-aid wearers

This study reports the prescribed, clinician-fit, coupler gain and the user-adjusted, as-worn coupler gain measured in 55 adults ranging in age from 60 to 83 years (M = 72.2 years). All participants were fit with linear, output-limiting compression, Class D circuits in full-concha, in-the-ear (ITE) shells. The NAL-R prescription rationale was used to generate target real-ear insertion gain (REIG) and coupler gain values. The clinician-fit gain was measured when the hearing aid was dispensed initially and was found to be a close match to the prescribed coupler gain. Both clinician-fit and as-worn gain were measured subsequently at approximately 2 weeks, 1 month, 6 months, and 1 year after the initial fitting. As-worn gain was measured as soon as the participant returned to the clinic for one of the follow-up visits by simply removing the hearing aids and placing them in the test chamber without any adjustments in volume control. At each follow-up session, the clinician then inspected the hearing aids, evaluated the instruments electroacoustically, readjusted the volume control to the setting used to match the prescribed gain in the initial fit, and measured the clinician-fit coupler gain once again. Results revealed that, despite the capability of the hearing aid to achieve coupler gain that is a close match to the prescribed gain, these users consistently selected as-worn gain that was generally 6-9 dB below that prescribed by the NAL-R formula. Of this 6-9 dB disparity, however, as much as 3-6 dB could be due to binaural summation effects not taken into consideration in the NAL-R prescriptive formula. In addition, 5.4% of the time, the hearing aids were found to be in less than ideal operating condition when removed for the as-worn gain measurements (e.g., weak or dead battery, cerumen occluding the sound bore, telecoil switch in the incorrect position).