Distribution characteristics of normal pure-tone thresholds

Abstract

Objective: This study examined the statistical properties of normal air-conduction thresholds obtained with automated and manual audiometry to test the hypothesis that thresholds are normally distributed and to examine the distributions for evidence of bias in manual testing. Design: Four databases were mined for normal thresholds. One contained audiograms obtained with an automated method. The other three were obtained with manual audiometry. Frequency distributions were examined for four test frequencies (250, 500, 1000, and 2000 Hz). Study sample: The analysis is based on 317 569 threshold determinations of 80 547 subjects from four clinical databases. Results: Frequency distributions of thresholds obtained with automated audiometry are normal in form. Corrected for age, the mean thresholds are within 1.5 dB of reference equivalent threshold sound pressure levels. Frequency distributions of thresholds obtained by manual audiometry are shifted toward higher thresholds. Two of the three datasets obtained by manual audiometry are positively skewed. Conclusions: The positive shift and skew of the manual audiometry data may result from tester bias. The striking scarcity of thresholds below 0 dB HL suggests that audiologists place less importance on identifying low thresholds than they do for higher-level thresholds. We refer to this as the Good enough bias and suggest that it may be responsible for differences in distributions of thresholds obtained by automated and manual audiometry.

Key Words::

• Audiometry
• automated audiometry
• pure-tone thresholds
• hearing
• normal hearing
• hearing test
• air conduction
• threshold
• bias

Acknowledgements

Portions of this work were supported by grant RC3DC010986 from the National Institutes of Deafness and Other Communication Disorders. The Rehabilitation Research and Development Service of the U.S. Department of Veterans Affairs supported this work through the Auditory and Vestibular Dysfunction Research Enhancement Award Program (REAP) and a Senior Research Career Scientist award to the second author. Appreciation is extended to Kevin Quitmeyer, Pam Urrutia, and Mary Ann Blumenthal from the Denver Acquisition and Logistics Center who extracted the VA archived data. Dr. Michael Hunter and his team at the Busselton Health Study provided assistance in collecting the Busselton data. The contents of this report do not represent the views of the Department of Veterans Affairs or the United States Government.

Note

Declaration of interest: AMTAS intellectual property is owned by Audiology Incorporated (AI) in which the first and last author have commercial interests. That intellectual property may be incorporated into commercial products. The other authors report no conflicts of interest.

Notes

1. Although Bell is widely credited with the invention of the telephone, a case has been made for Antonio Meucci (1808–1889) for his ʽtelettrofono” which was submitted to the U.S. Patent Office in 1871. See Meucci, 2010.