Apdex

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. Based on user experience satisfaction by measuring the response time of web applications and services, its role is to counterbalance response time averages and percentiles which can be misleading when there are extreme data points.

Definition

Apdex is a numerical measure of user satisfaction with the performance of enterprise web applications. It converts many measurements into one number on a uniform scale on the [0;1] interval:

• 0 = no users satisfied

• 1 = all users satisfied

First, define a time threshold—T—separating satisfactory response times from unsatisfactory response times from your web application or service. With one threshold you can then define three categories:

• Satisfied requests have a response time below T.

• Tolerated requests have a response time equal to or above T and below or equal to 4T.

• Frustrated requests have a response time above 4T or return an error.

Once the threshold is defined and your requests are categorized, the Apdex is defined as:

Apdex = (Satisfied requests+(Tolerated requests)/2) / Total requests

Selecting the correct threshold is important because the Frustrated requests are 4 times slower than “normal”. If T=3 the user waits 3 seconds for a page to load but does not tolerate waiting 12 seconds.

Apdex thresholds must be set by administrators, per service, before Apdex scores are calculated.