Table 1. WHO's Grades of hearing impairment

Grade of impairment	Corresponding audiometric ISO value	Performance
0: No impairment	25㏈ or better	No or very slight hearing problems. Able to hear whispers.
1: Slight impairment	26-40㏈	Able to hear and repeat words spoken in normal voice at 1 meter.
2: Moderate impairment	41-60㏈	Able to hear and repeat words in raised voce at 1 meter.
3: Severe impairment	61-80㏈	Able to hear some words when shouted into better ear.
4: Profound impairment including deafness	81㏈ or greater	Unable to hear and understand even a shouted voice.

Audiometric ISO value = The average of hearing level at 500, 1000, 2000 and 400㎐