APDEX(Application Performance inDEX) An open standard for measuring user satisfaction. It is typically used to rate the responsiveness of an application such as how long it takes to get a result after clicking the mouse. Users rate their perception as "satisfied," "tolerating" or "frustrated." The APDEX formula is the number of satisfied users plus half the tolerating users divided by all users. Oddly enough, frustrated users are ignored. The result is a rating from 0.0 (nobody satisfied) to 1.0 (everybody satisfied). A score of 0.5 would be middle of the road. For more information, visit www.apdex.org.