A clinical comparative investigation of a non-linear versus linear hearing aid.

The objective of this study was to compare the effect and performance of a hearing aid (HA) having a non-linear amplification below 1600 Hz (test HA) with a linear amplifying HA (control HA), aiming towards identical target groups of hearing-disabled people. The investigation was designed as a single-blind crossover interview study, i.e. the interviewer was blind. Thirty-two experienced HA users at a median age of 74 years participated. The observation period was 6-8 weeks for both HAs. For several evaluation parameters the participants found the test HA superior to the control HA, and a significantly better effect of the test HA was indicated in person-to-person conversation in quiet surroundings. Also, quality of sound was significantly better in the test HA, and thus these parameters support the test HA, being preferred by 75%. No significant differences were found in the objectively evaluated parameter, i.e. speech recognition score in background noise (SRSN: S/N = 0) between the two aids. A one-year follow-up examination of those preferring the test HA demonstrated continuously frequent use and satisfaction with the automatic volume control. It is concluded that skilled HA users with a wide range of hearing impairment at an age of 60-80 years prefer a non-linear HA to their current linear HA when fitted monaurally--however, a certain bias in the unblinded test subjects cannot be excluded.