Analysis of hearing aid fittings using insertion gain measurements

Insertion gain was measured in 166 persons after they were fitted with a hearing aid according to the Swedish prescription guidelines. Fitting was considered inadequate (1) when the levels of the long-term RMS speech spectrum were not amplified above the tone threshold at 1.0, 1.5 and 2.0 kHz, or (2) when the speech peak levels did not exceed the tone thresholds at 3.0 and 4.0 kHz. At least 40% of the subjects were found to have inadequate amplification according to these criteria. This number increased further when the measured insertion gain was compared with the gain recommended by other investigators. Our results indicate that real ear insertion gain measurements should be introduced as a routine clinical procedure in the fitting of hearing aids.