TNO Inst. of Preventive Health Care, P.O. Box 124, 2300 AC Leiden, The Netherlands
To determine noise-induced hearing loss in otologically unselected populations exposed to occupational and/or nonoccupational noise, hearing threshold levels of these populations should be compared with those of a comparison population. To that aim, based on two Netherlands databases, a calculation scheme for hearing threshold levels of otologically unselected comparison populations has been developed. In this scheme, median hearing thresholds are taken equal to 2 dB plus the median hearing threshold levels given in database ISO A [ISO 7029 and Annex A of ISO 1999:1990 (E)] for frequencies between 500 and 6000 Hz. The hearing thresholds exceeded in 90% of the comparison population are equal to those in database ISO A, and the hearing thresholds levels exceeded in 10% of the comparison population are 6 dB plus those given in database ISO A. The calculation scheme fits very well the data of otologically unscreened male comparison populations in Germany [Irion (1983); Pfeiffer (1985)], France [Thierry (1988)], Hong Kong [Evans (1982)], Sweden [Hansson (1992)], and a black population in the USA [Driscoll and Royster (1984)].