Abstract:

The ability to discern between etiological factors in hearing impairment depends upon using an accurate and fair method for apportionment. The popular method for division of causation assumes: (1) that pure tone audiometric information reflects the condition of the hearing mechanism (validity); and (2) that the AMA handicap percentage calculations accurately represent the degree of handicap experienced by a given individual (validity, again). Neither of these assumptions can be substantiated. Histological evidence contradicts the notion that pure tone hearing testing gives adequate information on the true status and condition of inner ear sensory neuroepithelium for purposes of apportionment. To ``break apart'' (allocate) complex causation in audiometric data, the effects of etiologies must be ``additive'' or they must combine in some measurable fashion. There is no convincing evidence regarding the additive nature of two or more etiologies with respect to pure tone audiometric data. In fact, hair cell injury and destruction is due to complex interaction between etiological factors.