The literature review alone gives limited information concerning the extent of the problem of hearing impairment in adult populations in the target countries. Likewise, there are only a few studies fulfilling strict scientific criteria on hearing aid outcome, and although many of the studies excluded in the literature search may have clinical relevance at specific sites, they cannot be generalised into larger populations. Even fewer studies correlate rehabilitation outcome with the degree of hearing impairment, disability or handicap.
The survey indicated striking differences between the countries. The numbers of hearing aids fitted annually per 1000 persons vary from 2.72 in Finland to 12.30 in Denmark. A significant proportion of the hearing impaired in the Nordic countries and in the United Kingdom have not sought help and do not possess or use a hearing aid. About 3.5% of the population of Denmark and the United Kingdom use a hearing aid; the figures being 2.8% in Norway and 1.0% in Finland. None of these approaches the figure of 5% of the population who are estimated to have >= 45 dB hearing impairment in both ears. Also, wide variations in the estimated expenditure per person with a hearing aid exist. In Finland, the expenditure per person with a hearing aid was estimated to be double that of Norway and Denmark and nearly tenfold that of the United Kingdom.
