Effects of pre-existing hearing loss on proposed ANSI S12.13 outcomes for characterizing hearing conservation program effectiveness: follow-up investigation.

Draft ANSI S12.13 1991 Standard Evaluating the Effectiveness of Hearing Conservation Programs presents statistical protocols purportedly sensitive to temporary threshold shift (TTS) in occupational hearing conservation program (HCP) audiometric databases. Because it is well established that less TTS is found in humans with hearing loss than in those with essentially normal hearing, one might predict baseline hearing level to be a confounding variable in interpreting ANSI S12.13 outcomes, with better-hearing industrial populations tending to demonstrate greater year-to-year audiometric variability than poorer-hearing groups. However, in a large industrial sample from the public domain audiometric database, poorer-hearing groups systematically demonstrated greater audiometric threshold variability than better-hearing groups, and ANSI S12.13 outcome magnitudes were highly positively correlated to baseline hearing levels. These findings generally do not support notions that ANSI S12.13 outcomes clearly provide indirect measures of TTS. HCP managers should exercise extreme caution in interpreting ANSI S12.13 outcomes to rate overall program performance. In particular, HCP managers should not rely upon these outcomes for decisions regarding hearing protection policies without careful consideration of pre-existing hearing loss in the populations involved.