apdex
also: Application Performance Index
Apdex (Application Performance Index) is a standardized metric that measures user satisfaction with application response time by categorizing responses as satisfied, tolerating, or frustrated based on predefined thresholds.
Apdex is an open standard developed to quantify application performance from the end-user perspective. It converts response time measurements into a numerical score between 0 and 1, where 1 represents perfect performance and 0 represents completely unacceptable performance.
The metric classifies responses into three categories: satisfied (response time ≤ T seconds), tolerating (response time between T and 4T seconds), and frustrated (response time > 4T seconds). The threshold T is configurable based on your application's requirements.
For example, if T is set to 1 second, a response in 0.5 seconds is satisfied, a response in 2 seconds is tolerating, and a response in 5 seconds is frustrated. The Apdex score is calculated as: (satisfied + tolerating/2) / total_samples.
Apdex is widely used in application performance monitoring (APM) tools like New Relic and Datadog to provide stakeholders with a simple, actionable metric for tracking user experience quality over time.