When evaluating cases of occupational hearing loss, one must distinguish between Medical and Legal Causation.   Medical Causation calls for scientific certainty, but Legal Causation only needs to be within a reasonable degree of medical certainty.  In some settings, only a more likely than not or greater than 50% likelihood is needed.

Presbycusis is hearing loss associated with aging.  In the medical-legal context, it is the "non-occupational" hearing loss, or "nosocusis" as described by Kryter in 1983, which the average individual of a certain age has.  Compensation for presbycusis may be performed when evaluating occupational hearing losses.  Go To Presbycusis Calculator

Often workers have a preexisting hearing loss when they begin employment.  Many years later, upon retirement, the hearing loss is worse and the question is raised:  Is the worker's hearing loss at retirement due to added occupational noise exposure, or is it just the combination of the worker's pre-employment hearing loss and other environmental factors.  The Age Projection Calculator or Master Calculator can give guidance to this question.  This calculator can also be used to project the worker's post-employment audiogram into the future and determine the likely hearing impairment at any given age.  (The Master Calculator and Age Projection Calculators will determine the degree of presbycusis in the initial audiogram.  Subtract these values from the presbycusis for the projected age; then add the difference to the thresholds in the initial audiogram, thus, calculating the projected audiogram.  All projected thresholds are also off-set by the ISO-1999 compression factor and truncated at 100 dB.)