One of the biggest obstacles in the way of an adequate statistical study of the effects of occupational noise on hearing acuity has been the scarcity of reliable long-term audiometric observations on industrial personnel. The effect of very high noise levels can be detected in a short period of time, as illustrated by McCoy's1 one-year study of chipping workers, but knowledge of the effects of lower noise levels requires proportionately longer periods of observation. Lacking satisfactory follow-up data, many investigators2-7 have been compelled to draw inferences on the basis of current audiograms taken on noise-exposed workers, using as control data the audiograms of other employees in the plant or the findings of large-scale population surveys.
This method of study has two drawbacks. First, the investigator must take into account the amount of hearing loss that has been incurred as a result of various types of acoustic trauma