5.1 Why Audiometry Has Inherent Variation
Audiometry and Calibration
- A study analyzing four different commercially available, recently calibrated audiometers found a high level of test-retest variability.
- Maximum variation of sound pressure level at the ear for the same tone presentation was 21 decibels.
- A particularly high level of variation was found at 6 kHz for all audiometers.
- An audiometer using attenuating cups (common in industrial screening) exhibited significantly higher variation than those with standard supra-aural headphones.
- Calibration standards (BS EN ISO 8253 series) establish strict tolerance limits for audiometric equipment. However, even within these tolerances, small variations exist.
What it is: Audiometry is the clinical test used to measure a person's hearing threshold. However, the results are subject to variability. This variation can come from the equipment itself (even when calibrated), the test environment (background noise), and the subject's physiological and psychological state (e.g., tinnitus, attention).
A study analyzing four different commercially available, recently calibrated audiometers found a high level of test-retest variability.
Maximum variation of sound pressure level at the ear for the same tone presentation was 21 decibels.
A particularly high level of variation was found at 6 kHz for all audiometers.
An audiometer using attenuating cups (common in industrial screening) exhibited significantly higher variation than those with standard supra-aural headphones.
Calibration standards (BS EN ISO 8253 series) establish strict tolerance limits for audiometric equipment. However, even within these tolerances, small variations exist.
The study highlights that the calibration process itself is not always accredited, leaving the standard open to interpretation and potential errors.
Calibration is typically required annually, but the study shows that even recently calibrated equipment can exhibit significant variability.
Why it matters: A change in an audiogram between tests does not automatically signify a true change in hearing; it could be within the measurement's margin of error. Understanding this is crucial for correctly interpreting health surveillance results and not confusing audiometric variability with a failure of hearing protection. Related: [#cnawr-health-surveillance](#cnawr-health-surveillance).