Current application performance-measurement tools have several limitations. Each has its own definition of performance, produces too many confusing or conflicting numbers, and lacks a simple summary result. IT managers have no insight into the performance that matters - users' experience with mission-critical applications.

A consortium of companies called the Apdex Alliance is developing the Application Performance Index (Apdex) to specify a uniform way to measure and report on the user experience. Apdex is a numerical measure of user satisfaction with the performance of enterprise applications. The metric gauges the effectiveness of IT investments, and helps CIOs and other executives understand whether their applications are delivering on promises or just operating.

Implemented as a reporting window for current products, Apdex converts application response time measurements from many tools and services into a single number using a scale of 0-to-1 (0 equals no users satisfied, 1 equals all users satisfied).

Task response time is defined as the elapsed time between when a user does something (mouse click, enter, return) and when the system (client, network, servers) responds so that a user can proceed with the process. These waiting periods define the "responsiveness" of the application. The index is based on three zones of application responsiveness:

• Satisfied : The user is fully productive. This is the target time (T seconds), a period during which users are not impeded by application response time - for example, 3 seconds.
• Tolerating : The user notices performance lagging within responses greater than T but continues the process - say, between 3 and 12 seconds.
• Frustrated : Performance with a response time greater than F seconds is unacceptable, and users may abandon the process. F equals T X 4, or 12 seconds in this example.

The Apdex formula is the number of satisfied samples plus half of the tolerating samples, divided by the number of all samples. The result is a fraction that ranges from 0 to 1.

Say there are 100 samples with a target time, T, of 3 seconds. Sixty samples are below 3 seconds, 30 samples are between 3 and 12 seconds, and the remaining 10 samples are above 12 seconds. The Apdex calculation is as follows: