Concept of the notional person in the assessment of hearing disability

Medicolegal assessment in relation to a claim for hearing damage requires an equitable baseline against which to compare the state of hearing of the claimant. This baseline, or 'notional person', should match the claimant in every respect save for the cause of the hearing loss. The amount of compensation is determined from the difference between the percentage disability of the claimant and that of the 'notional person'. These percentages are, in turn, calculated from the respective hearing threshold levels. In the particular case of occupational noise-induced hearing loss there are, in principle, two ways of proceeding. One way is to estimate directly the noise-induced threshold shift which would result from the noise exposure and to subtract this from the claimant's measured threshold level; in practice the noise exposure is rarely known with the necessary accuracy. The alternative method is to construct the notional person's threshold level by adding together all the non-compensable components of hearing loss known to exist in the claimant. These may include: conductive hearing loss together with any sensorineural sequelae, sensorineural loss specifically attributable to identifiable accident or disease, pure biological ageing, any pathological overlay due to deficiencies of aural or general health, the effect of non-occupational noise, and the socioeconomic status of the claimant. Once these components are summed, whatever remains unaccounted for is deemed to be due to the occupational noise. An International Standard (ISO 7029) exists for the biological ageing component but it is specific to 'otologically normal' persons and on its own does not account for all the time-dependent hearing losses found in a typical claimant. Moreover, the term 'otologically normal', although defined in the relevant Standards, leads to varying interpretations, even to misunderstandings. In practice, the equitable baseline for the disability assessment is most often a 'typical' rather than an 'otologically normal' person in the Standards sense. This paper offers guidance for estimating the combined time-dependent threshold shift in these commonly occurring cases, based on the use of published survey data. It is recommended that a presumption of 'typical hearing' should be made unless the claimant in question can be specifically verified as 'otologically normal'.