Hearing Impairment Equations
It is common for an individual to want to know what percent hearing loss they have based on the results of a hearing test. Most calculations to determine this hearing impairment number incorporate the main frequencies that contribute to speech understanding which encompass 500 Hz to 4000 Hz that is weighted towards the better hearing ear. Over the years, several different formulas have been suggested and are summarized in the chart below (equation following the chart):
Formula | Frequencies (Hz) | Low Fence (dB) | High Fence (dB) | Better Ear Ratio |
---|---|---|---|---|
AAO 1979 | 500, 1000, 2000, 3000 | 25 | 92 | 5 : 1 |
AAOO 1959 | 500, 1000, 2000 | 25 | 92 | 5 : 1 |
NIOSH-FECA 1972 | 1000, 2000, 3000 | 25 | 92 | 5 : 1 |
NIOSH-1997 | 1000, 2000, 3000, 4000 | 25 | 92 | 5 : 1 |
British Society of Audiology | 500, 1000, 2000, 4000 | 25 | 92 | 5 : 1 |
Wisconsin (CHABA*) | 1000, 2000, 3000 | 35 | 92 | 4 : 1 |
Oregon | 500, 1000, 2000, 4000, 6000 | 25 | 92 | 5 : 1 |
Ireland | 500, 1000, 2000, 4000 | 20 | 100 | 4 : 1 |
DOT CDL | 500, 1000, 2000 | see note #1 |
The equation to calculate the percent impairment using the values in the chart is as follows:
% Loss for One Ear = ([AVG of ({dB for Hz#1}, {dB for Hz#2}, {dB for Hz#3}, etc)] - {Low Fence dB}) x 1.5)
% Combined Hearing Loss 5:1 Equation = [(% better hearing ear x 5) + (% worse ear)] / 6
Note #1: Considered a PASS if the average hearing loss in the better ear is greater than 40 dB at 500 Hz, 1000 Hz, and 2000 Hz with or without a hearing aid.