Abstract:
Noise-induced hearing loss is a major cause of permanent disability in working populations, and it is an increasing contributor to workers' compensation costs. The most widely used method for defining whether impairment exists in individual cases of hearing loss was adopted by the American Medical Association in 1984, from guides published by the American Academy of Otolaryngology n 1979. However, there are a number of other impairment-evaluation methods, many of which are currently in use or have been considered for use by agencies involved in disability compensation. Although scientific information exists to support the validity of each method, the various methods can yield substantially different conclusions about the presence and degree of impairment in individuals with similar patterns and levels of hearing loss.
This study used audiometric surveillance data from a convenience sample of nuclear industry workers (n=25,271) to conduct descriptive and sensitivity analyses of the differences between selected representative impairment-evaluation methods, and the relative influence of individual components of such methods, on the determination of hearing impairment. The number of individuals determined to be impaired was influenced most by the hearing threshold level defined as 0% impairment (low fence), and, if utilized, the type of age-correction method. Among individuals determined to be impaired, the calculated level of impairment was influenced most by the hearing threshold level defined as 100% impairment (high fence) and the weighting applied to hearing threashold differences between ears (better:worse ear weighting).
A separate assessment of the median-based method for allocating impairment betyween age and noise exposure evaluated the necessary accuracy of historical information about noise exposure. The influence of inaccuracy in the estimated average noise level was relatively greater than for the duration of the exposure. However, at higher noise levels, a greater level of accurace was required of the estimate of noise exposure duration.
The findings of this study can provide useful guidance in future considerations of methods for determining impairment in individual cases of hearing loss. However, in such considerations, scientific evidence of validity should receive greater weight than population outcomes or costs.