Hearing impairment among adults--extent of the problemand scientific evidence on the outcome of hearing aidrehabilitation.

Scientific surveys on current and estimated prevalence of hearing impairment (HI) in adult populations (> or = 18 years ofage) in Denmark, Finland, Norway, Sweden and the United Kingdom, and scientific reports on the outcome of hearing aid (HA) rehabilitationworldwide were reviewed. Only a few of the studies meet strict scientific criteria, and many locally clinically relevant studiescannot be generalized to larger populations. Population-based studiesindicate an increase in prevalence of HI with age, but because ofdifferences in study populations and available national populationstatistics, the studies do not allow reliable comparisons betweencountries or estimation of future prevalence of HI. Studies on HAprescription or outcomes do not provide uniform data in favour ofnon-linear amplification, but they do show some subject preference forthe newer technology. No conclusions can be drawn regarding the degreeof HI and the effects of amplification. The literature review alonegives only limited information regarding the extent of the problem ofHI in adult populations in the target countries. Similarly, only a fewstudies on HA outcome meet strict scientific criteria and even fewerstudies correlate rehabilitation outcome with the degree of HI,disability or handicap.