What is "articulation index"

In audiology, the Articulation Index (AI) is a tool used to predict the amount of speech that is audible to a patient with a specific hearing loss. The AI figure for a given patient can range from zero to one, representing the proportion of the average speech signal that is audible. The closer the AI is to one, or 100 percent, the better the person should be able to hear speech. The calculation is also used in industrial settings for the design of safety devices, such as flight helmets, where audio signals are required to be clearly heard.