Some implications of audiological measures in the population for binaural aiding strategies.

The health-economic and statistical problems involved in concluding in favour of provision of binaural aids for subsets of the hearing-impaired are outlined. A positive mean binaural advantage is a first step only; an adequate way of handling individual differences must be the second step. Data comparing two population studies show an appreciable binaural advantage for speech in noise; age differentially affects the binaural advantage in males only, which may explain contradictions in the literature. Evidence is obtained that binaural sentence understanding in noise does depend materially upon symmetry of hearing, despite a generally minimal role for the worse ear a statistical predictor. Detailed results suggest that 15 dB asymmetry at threshold should be used as a contraindication to binaural fitting. At lesser degrees of asymmetry (around 10 dB), asymmetry alone is not an adequate basis for generalised differential prognosis for binaural aids because of various supra-threshold considerations. Hence binaural integration should be directly assessed both in field trials of binaural aiding, and in clinical practice.