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  Apdex Overview
"Apdex represents a new milestone in application analysis. The network management industry needs an agreed upon standard to reflect the experience of the end-user for everyday applications. Apdex is a natural extension to our tried and proven Application Response Time analysis already incorporated into our existing products."

Scott Haugdahl
Chief Technology Officer
WildPackets, Inc.
Apdex (Application Performance Index) is an open standard developed by an alliance of companies that defines a standardized method to report, benchmark, and track application performance.

The Problem
Enterprises are swimming in IT performance numbers, but have no insight into how well their applications perform from a business point of view. Response time values do not reveal whether users are productive, and a greater number of samples leads to confusion. Averaging the samples washes out significant details about frustration with slow response times. Time values are not uniform across different applications. There should be a better way to analyze and measure what matters.

The Solution
Apdex is a numerical measure of user satisfaction with the performance of enterprise applications. It converts many measurements into one number on a uniform scale of 0-to-1 (0 = no users satisfied, 1 = all users satisfied). This metric can be applied to any source of end-user performance measurements. If you have a measurement tool that gathers timing data similar to what a motivated end-user could gather with a stopwatch, then you can use this metric. Apdex fills the gap between timing data and insight by specifying a uniform way to measure and report on the user experience.

The index translates many individual response times, measured at the user-task level, into a single number. A Task is an individual interaction with the system, within a larger process. Task response time is defined as the elapsed time between when a user does something (mouse click, hits enter or return, etc) and when the system (client, network, servers) responds such that the user can proceed with the process. This is the time during which the human is waiting for the system. These individual waiting periods are what define the "responsiveness" of the application to the user.

How it Works
Performance measurement and reporting tools that support Apdex will conform to a specification developed by the Alliance that will be publicly available. It specifies a process that Apdex compliant tools and services will implement. A key attribute of the process is simplicity. What follows is a basic overview.

The index is based on three zones of application responsiveness:

  • Satisfied:  The user is fully productive. This represents the time value (T seconds) below which users are not impeded by application response time.
  • Tolerating:  The user notices performance lagging within responses greater than T, but continues the process.
  • Frustrated:  Performance with a response time greater than F seconds is unacceptable, and users may abandon the process.

The Apdex formula is the number of satisfied samples plus half of the tolerating samples plus none of the frustrated samples, divided by all the samples:

So it is easy to see how this ratio is always directly related to users' perceptions of satisfactory application responsiveness. To understand the full meaning of the ratio, it is always presented as a decimal value with a sub-script representing the target time T. For example, if there are 100 samples with a target time of 3 seconds, where 60 are below 3 seconds, 30 are between 3 and 12 seconds, and the remaining 10 are above 12 seconds, the Apdex is: