Frequency response differences of four gain-equalized hearing aid prescription formulae.

The relative differences between the NAL, Berger, Lybarger und POGO hearing aid prescriptions were evaluated using 8 hypothetical audiograms and 81 actual hearing loss cases. The gains of the prescriptions were equalized, making the prescriptions maximally similar, as would presumably occur when the aids are worn. Statistically significant differences in the frequency responses of the prescriptions were found, with up to 17 dB gain difference observed; however, the gain differences at any given frequency were generally less than 8 dB. Sharply sloping hearing losses had the greatest differences between prescriptions. The NAL and Berger prescriptions were most disparate, while POGO and Lybarger were most similar. As large differences in prescribed gain are rare, research into the relevance of such small differences in frequency response is advocated as a precursor to study of the optimal prescription formula