Custom-molded earplug performance: a retrospective study

The purpose of this study was to determine the effectiveness of custom-molded earplugs in preventing hearing threshold shifts over a long period of time. A stepwise regression analysis was employed to accomodate job related variables including workplace noise level, demographic elements including age, and factors related to hearing including ear history. These variables would be expected to exert considerable influence on hearing threshold shifts. However, workplace noise level absorbed unexpected small amounts of variation in hearing threshold shifts for the textile worker subjects (N = 1517) even when noise level was entered as the only variable on the first step for each analysis. And, baseline hearing values absorbed unexpected large amounts even when entered on the last step. An argument based on these findings is presented suggesting that custom-fitted hearing protection was effective in preventing substantial changes in hearing threshold level during the period of this investigation.