**Parent Topic**: [[Software/README]] ## What It Is The Application Performance Index (Apdex) is "a measurement of how often the application's performance and availability are acceptable" — easy to calculate and comparable across contexts. It collapses a latency distribution into a single 0-to-1 score. ## How to Calculate 1. Set a performance target (e.g. "the login page should load in two seconds"). 2. Bucket each loaded page into three ratings: **satisfied** (within target), **tolerating** (within 4× the target), or **frustrated** (over 4× the target, or failed to load). 3. Score = (satisfied + tolerating/2) / total, yielding 0 to 1, where 1 = every transaction met the target and 0 = every user was frustrated. ## Why It Works "The strongest argument for Apdex is math": you roll scores up across sites, pages, or time periods just by totaling the satisfied/tolerating/frustrated counts, even when different parts of the site have different targets, and whether you have a handful of measurements or thousands per second. And it's executive-legible — "most executives won't understand anything more complex than a golf score." It's also the bridge for [[Correlate Performance with Analytics]] (mark visits by Apdex level). Builds on [[Use Percentiles Not Averages]] as a digestible alternative to raw distributions. --- *Source: [[Web Operations]] (Allspaw & Robbins, O'Reilly 2010) — Ch 11 — How Your Visitors Feel: User-Facing Metrics*