scope:

This document provides descriptive statistics of the hearing threshold deviation for populations of otologically normal persons of various ages under monaural earphone listening conditions. It specifies the following, for populations within the age limits from 18 years to 80 years for the range of audiometric frequencies from 125 Hz to 8 000 Hz:

a) the expected median value of hearing thresholds given relative to the median hearing threshold at the age of 18 years;

b) the expected statistical distribution above and below the median value.

For the frequencies from 3 000 Hz to 8 000 Hz, the median and statistical distribution for populations above 70 years are presented for information only.

This document also provides for information the expected median values at audiometric frequencies from 9 000 Hz to 12 500 Hz within the age limits from 22 years to 80 years.

The data are applicable for estimating the amount of hearing loss caused by a specific agent in a population. Such a comparison is valid if the population under study consists of persons who are otologically normal except for the effect of the specific agent. Noise exposure is an example of a specific agent and for this application, selected data from this document are referred to as "database A" in ISO 1999.

NOTE 1 ISO 1999:2013, Database A is based on a previous edition of ISO 7029.

The data may also be used to assess an individual's hearing in relation to the distribution of hearing thresholds which is normal for the person's age group. However, it is not possible to determine for an individual precisely which part of an observed hearing loss is attributable to an accumulation of detrimental effects on the hearing which increase with age, and which part has been caused by other factors such as noise.

The hearing threshold deviation as defined herein and the hearing threshold level as defined in other International Standards (ISO 389-1, ISO 389-2, ISO 389-5, ISO 389-8, ISO 8253-1, ISO 8253-2, IEC 60645- 1) express the hearing threshold of an individual or an individual ear, respectively, relative to

- the expected median hearing threshold of 18-year-old age group of the same gender, or

- a reference zero level specified in various parts of ISO 389.

To the extent that the reference zero level represents the median of the 18-year-old population, the values of the two terms will be the same.

NOTE 2 The values of these two are not always the same for some reasons. One reason is that the reference zero level has been determined based on the hearing threshold levels of persons older than 18 years, including those aged up to 25 years or to 30 years, who have slightly worse hearing sensitivity on average.

NOTE 3 ISO 28961 specifies the expected statistical distribution of hearing thresholds, expressed in sound pressure level in decibels, for populations of otologically normal persons of the age from 18 years to 25 years under binaural, free-field listening conditions. It enables the calculation not only at audiometric frequencies, but also for other frequencies at one-third-octave intervals from 20 Hz to 16 000 Hz.