Predictive validity of a retrospective measure of noise exposure

To investigate the validity of measures of noise exposure derived retrospectively for a cohort of nuclear energy workers for the period 1950-98, by investigating their ability to predict hearing loss.

Subjects were men aged 45-65 chosen from a larger group of employees--assembled for a nested case-control study of noise and death from ischaemic heart disease--who had had at least one audiogram after at least five years' work. Average hearing loss, across both ears and the frequencies 0.5, 1, 2, and 4 kHz, was calculated from the last audiogram for each man. Previous noise exposure at work was assessed retrospectively by three hygienists using work histories, noise survey records from 1965-98, and judgement about use of hearing protection devices. Smoking and age at the time of the audiogram were extracted from records. Differences in hearing loss between men categorised by cumulative noise exposure were assessed after controlling for age, smoking, year of test, and previous test experience.

There were 186 and 150 eligible subjects at sites A and B of the company respectively who were employed for an average of 20 years. Compared to men with less than one year's exposure to levels of 85dB(A) or greater, hearing loss was greater by 3.7 dB (90% CI -2.6 to 10.1), 3.8 dB (90% CI -2.6 to 10.3), 7.0 dB (90% CI 1.1 to 12.9) and 10.1 dB (90% CI 4.2 to 16.0) in the lowest to highest categories of cumulative noise exposure at site B. In contrast, at site A, the corresponding figures were -2.2 dB, -2.4 dB, -1.8 dB, and -4.4 dB, with no confidence interval excluding zero.

Noise estimation at one site was shown to have predictive validity in terms of hearing loss, but not at the other site. Reasons for the differences between sites are discussed.