Evaluation of prescriptive fitting

The purpose of this study was to determine the minimum tolerance needed when choosing a manufacturer who custom-built analog circuitry for all-in-the-ear hearing aids to match a popular prescriptive amplification formula. Given the tolerance, a second purpose was to evaluate fitting success by calculating the differences in prescribed versus preferred gain and pre- versus postfitting perceived benefits. Eight elderly adults with mild to moderate sensorineural hearing losses participated. Real ear measurements were obtained via a probe-tube microphone system. Even when providing for the optimal scenario of custom-building the circuitry, the inherent limitations of analog technology allowed no better than a +/- 12 dB electroacoustic match to prescribed gain. Although the minimum tolerance found was less than previous studies, it was still considered excessive given the differences in prescribed gain among formulae. Regardless of the large tolerance and a preference for less gain than prescribed, the subjects reported substantial benefit with the fitting approach.