ISO 28961, which describes the statistical distribution of hearing thresholds of otologically normal young persons, was established in 2012. The thresholds are those for pure tones of frontal incidence under binaural listening conditions in a free field. Percentiles of the threshold distribution are calculable as a function of frequency from 20 Hz to 16,000 Hz. This international standard is based on the study results of the present authors, who estimated the form of individual distribution using threshold data in their experiments and those in literature adopted in ISO 226 and ISO 389-7. However, because the results were published separately in four journal papers, users of the standard may encounter difficulty in understanding the process of how the threshold data have been integrated and how the threshold distribution has been determined. Therefore, the authors summarize them in this review paper and present an outline of the threshold distribution estimation so that the standard will be understood correctly and used widely.
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