A graphical method for calculating the speech intelligibility index and measuring hearing disability from audiograms.

The speech intelligibility index (SII) is interpreted as the proportion of total speech information available to the listener's ear for a given speech material. Consequently, SII varies in the range 0-1. A simple graphical method for determining SII for monaural listening at 1 m distance from a talker producing "average speech" (or PB-words) at normal speech effort is described. The speech area is visualized by 10 x 10 = 100 points in the audiogram form, each point contributing 0.01 to the SII. The SII thus equals 0.01 times the number of points in the audible range. A sensorineural hearing loss gives rise to an additional loss in speech recognition due to reduced frequency discrimination and time resolving ability. This suprathreshold deficit is corrected for, if the SII contribution in each frequency band is multiplied with a hearing threshold level dependent "desensitization factor". The SII is related to the intelligibility of speech, and may be used to evaluate a hearing disability.