The relative contributions of occupational noise and aging in individual cases of hearing loss.

A method is proposed for allocation of hearing handicap between noise and aging in individual cases when noise exposure level and duration are known or can be estimated. A recently published international standard (ISO-1999, 1990) provides statistical models for hearing threshold changes associated with aging and noise exposure. When an individual's hearing threshold level exceeds the sum of the median levels expected given that individual's age, gender, exposure level, and exposure duration, the appropriate allocation depends on the correlation between age-related and noise-induced changes. However, the differences in allocation between assumptions of perfect and absent correlation are small. Only very small errors result from calculating the allocation based on median expectations for noise and aging. In most cases, age-related changes exceed noise-induced changes for the 0.5, 1, 2, and 3 kHz pure-tone average; for men age 65, this is true for all exposure levels below 100 dBA.