Quantification of hearing disability for medicolegal purposes based on self-rating

Current practice for medicolegal assessment of individuals entails the use of an impairment measure obtained from average hearing threshold levels as a surrogate for hearing disability, and conversion of the surrogate to disability via a formula. Several different formulae are in use, but none is based explicitly on experimental data. To address this lack of empirical foundation in the assessment process, numerical self-ratings of hearing ability by 2058 subjects with a wide range of hearing threshold levels who had taken part in the National Study of Hearing in the UK were analysed to examine their relation to average hearing threshold level. The relation between self-rated hearing disability (the complement of self-rated hearing ability) and hearing threshold level was found to be sigmoid in form, and could be closely modelled by a modified Gompertz function. Functions for the median, upper quartile and lower quartile disability ratings with hearing threshold level are presented in graphical, parametric and tabular form. The median function gives a quantitative foundation for medicolegal assessments.