Test-retest reliabiligy of real ear measurements for open canal hearing aid fittings

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Description/Abstract

When fitting hearing aids with conventional earmoulds using real ear measurements (REM) it is recommended to use the modified pressure with concurrent equalization method whereby a reference microphone is used to monitor the REM loudspeaker output level. The review of the literature indicates good test-retest reliability for REM using conventional earmoulds. However, in REM using open-fit, another sound field equalization method (the modified pressure with stored equalization method) should be used to minimize any inaccurate measurements resulting from the amplified sound leakage when the open-fit hearing aid is used. In addition the sound is delivered via a generic ear tip rather than a custom made earmould. Therefore, the test-retest reliability for conventional occluded earmould REM cannot be generalized to the open-fit measures.

Twenty otologically normal participants were tested to investigate short-term test-retest reliability for open-fit REM, and for conventional earmoulds at both 0o and 45o head-to-loudspeaker azimuths by performing repeated measurements at the same participant visit but after removing both the probe tube and the hearing aid and reinserting them. It was found that open-fit REM have good short-term test-retest reliability (mean 1.57 dB, SD 1.10 dB) at both azimuths and are in agreement with measured (mean 2.12 dB, SD 1.45 dB) and reported (SD ranged from 1 to 3.2 dB) conventional earmould REM test-retest variability values in the 0.25 to 4 kHz frequency range (Ringdahl A & Leijon A, 1984, The reliability of insertion gain measurements using probe microphones in the ear canal, Scandinavian Audiology, 13, 173-8). This finding is clinically significant as open fittings are widely fitted using REM to hearing impaired patients.