Is non-linear frequency compression amplification beneficial to adults and children with hearing loss? A systematic review

Objective: To conduct a systematic review of the benefits of non-linear frequency compression (NLFC) in adults and children. Design: Ten databases were searched for studies comparing the effects of NLFC and conventional processing (CP) for the period January 2008 to September 2017. Study sample: Twelve articles were included in this review: four adults and school-aged only, one pre-school only and three with both adults and school-aged children. Results: A two-stage process was implemented to grade the evidence. The individual studies were graded based on their study type (from 1 = highest quality of evidence to 5 = the lowest quality) and then sub-graded based on their quality (“a” for “good quality” or “b” for “lesser quality”). All studies were awarded 4a, except the single pre-school study, which was awarded 2a. The overall evidence for each population was graded based on the quality, quantity and consistency of the studies. The body of evidence was rated as very low for both adults and school-aged children, but high for pre-school children. Conclusion: The low number (and quality) of studies means that evidence supporting the benefit from NLFC is inconclusive. Further high-quality RCTs are required to provide a conclusive answer to this question.