Candidature for hearing aids: justification for the concept and a two-part audiometric criterion.

A definition of hearing aid candidature is required for planning and other purposes. The number of candidates in the population actually receiving an adequate fitting would provide the major index of whether audiology services achieve their major public health goal. Many diverse factors determine the benefit that an individual receives from a hearing aid, and hence could in principle be included in some composite criterion for appropriate candidature reflecting the cost-effectiveness of patterns of provision. However, the complexity of universal capture, on those fitted with hearing aids, of data giving full auditory and demographic characteristics is beyond current routine NHS information systems. The most powerful known determinant established to date both of auditory disability and benefit is average hearing threshold level (HTL). Hearing threshold levels are hence both a necessary part of the fitting process and, given the data from the National Study of Hearing, a sufficient basis for computing population prevalences of hearing characteristics and service uptake in the major demographic strata. We report epidemiological data on consultation about problems with ears or hearing and uptake of hearing aids, which lead us to recommend a two-part candidature criterion on hearing threshold levels (0.5-4.0 kHz average): EITHER (a) better ear HTL > or = 35 dB OR (b) (15 dB < or = better ear HTL < 35 dB) WHEN worse ear HTL > or = 45 dB. The asymmetric component (b) may appear contentious, but is directly supported both by the epidemiological data and by further clinical data on benefit measured as performance on speech-in-noise tests. The proposed criterion is not over-liberal in clinical or related technological terms, but against the high prevalence of impairments in the population, the current provision and uptake of hearing aids in the UK still appear modest (about 3.3% in the population, and just under one-third of those qualifying by our criterion). Whatever the means of providing hearing aids, authorities charged with meeting the needs of their populations require such statistical indicators to know whether service delivery is appropriately geared. They should not use such an indicator as a basis of entitlement, as there are certainly individuals outside the criterion who receive benefit from their hearing aids. Equally, technological progress could expand the boundaries of candidature.