The distribution of hearing threshold levels in the general population aged 18-30 years.

Hearing threshold levels at audiometric frequencies between 0.25 and 8 kHz were obtained by manual audiometry using 5-dB steps in adults aged 18-30 years, as part of a large random survey of hearing in the UK. After screening to ensure otological normality, including careful analysis of any noise exposure history, the median thresholds of the 241 screened subjects deviated from audiometric zero by an average of 4.3 dB over the frequencies from 0.5 to 4 kHz in the direction of poorer hearing. Even greater deviations were evident at 0.25, 6 and 8 kHz, consistent with the discrepancies between normal hearing threshold and ISO 389 standard reference zero that have been reported previously. Within the age band from 18 to 30 years, age did not influence hearing threshold levels. Socio-economic status defined by occupational group (manual or non-manual) had a significant effect at frequencies up to 2 kHz, with those in non-manual occupations having better hearing than those in manual occupations by an average of 2.4 dB, despite screening for middle-ear disease, noise exposure and other possibly confounding factors. In a screened sample, males had better hearing threshold levels than females, but this difference was sensitive to screening criteria. The unscreened sample had median hearing threshold levels that were at most 2 dB worse than the screened sample across the frequency range.