Test of the assumptions underlying comparative hearing aid evaluations

Comparative hearing aid evaluations using NU-6 monosyllabic word lists were administered to adults with predominately high-frequency sensorineural hearing impairments who were randomly assigned to one of two experiments. In the first, three instruments were used that were electroacoustically similar and appropriate to the patients' hearing losses. In the second, the three hearing aids employed were electroacoustically quite different. Following an initial comparative hearing aid evaluation, the patients used the instruments during a trial-use week after which they ranked the aids in terms of benefit provided in daily communication. Following the trial-use week, the comparative hearing aid evaluation was repeated. The results suggest that significant interaid performance differences on the hearing aid evaluation are not likely to occur very often when the aids being evaluated are relatively homogeneous electroacoustically. In contrast, when electroacoustically heterogeneous instruments are evaluated, significant performance differences may occur frequently. Under such circumstances, however, the same instrument(s) would likely provide the best performance to most patients. The results further suggest that the reliability of standard monosyllabic word lists may not be adequate to detect typical interaid differences that occur in a comparative hearing aid evaluation and that the performance hierarchy is likely to change as the patient adjusts to amplification. Finally, the comparative hearing aid evaluation will not be a good predictor of success in daily communication unless relatively large performance differences exist among the instruments.