Apdex (Application Performance Index) is used to measure the performance of software applications.
Its purpose is to convert measurements into insights about user satisfaction, by specifying a uniform way to analyze and report on the degree to which measured performance meets user expectations. It is based on counts of "satisfied", "tolerating", and "frustrated" users, given a maximum satisfactory response time t, a maximum tolerable response time 4t, and where users are assumed to be frustrated above 4t. The score is equivalent to a weighted average of these user counts with weights 1, 0.5, and 0, respectively.
The Apdex method converts many measurements into one number on a uniform scale of 0 to 1 (0 = no users satisfied, 1 = all users satisfied). The resulting Apdex score is a numerical measure of user satisfaction with the performance of enterprise applications. This metric can be used to report on any source of end-user performance measurements for which a performance objective has been defined.
Apdex T is the central value for Apdex—it is the response time above which a transaction is considered “tolerable.” You can define Apdex T values for each application, with separate values for app server and end-user browser performance. You can also define individual Apdex T thresholds for key transactions.