scope:

This Standard specifies, for the range of audiometric frequencies from 125 to 8000 Hz and for groups of otologically normal persons of a given age within the age limits of 18 to 70 years inclusive: a) the expected value of the median hearing threshold shift relative to a group of persons 18 years of age; b) the expected statistical distribution above and below the median value. The data in this International Standard are applicable as descriptive statistics of the hearing levels of populations of various ages. An example of this application is as a baseline of comparison for estimating the amount of hearing loss caused in a population due to a specific agent, for example, noise, and in this application the data of this International Standard are included as "Data Base A" in ISO 1999. The data may also be used to compare an individual's hearing with the normal distribution of the hearing threshold levels for the person's age group. In the audiological diagnosis of an individual person, it is, however not possible to determine precisely which changes of the hearing threshold level are attribute to an accumulation of detrimental effects upon the hearing increasing with age and which changes have been caused by other factors such as, for example, noise.