Re-estimated normal hearing threshold levels for pure tones using the calculation procedure of ISO 7029:2017

Objective: The objectives of this study were (1) to re-calculate hearing threshold levels (HTLs) for pure tones as described in an international standard, ISO 7029:2017, and (2) to explain the procedure of how HTLs in the standard had been derived. Design: Pure-tone hearing threshold data used for developing ISO 7029:2017 and additional data sets were combined to re-estimate median HTLs and the distribution of individual HTLs around the median. The calculation was done for audiometric frequencies from 125 Hz to 8000 Hz and extended high frequencies from 9000 Hz to 12,500 Hz for ages from 18 to 80 years. Study sample: Approximately 9000 men and 20,000 women employed in 15 studies in nine countries. They had been rigorously screened for hearing abnormalities. Results: A new set of median HTLs and distribution around the median was obtained as a function of age for males and females separately and compared with the estimates in ISO 7029. The differences among these threshold values were discussed. Conclusions: The calculation procedure described would help understand how the normative HTLs in ISO 7029:2017 had been obtained. Re-calculated HTLs could serve as a basis for the next edition of the standard that covers a wider range of population.