You may know the Apdex (Application Performance Index) to give a meaningful statement about an application's performance.

There are these three satisfaction zones, namely "satisfied", "tolerated" and "frustrated" with the corresponding thresholds T1 that separates the satisfied and tolerated zones and T2 that separates the tolerated and frustrated zones. Now, the Apdex formula says T2 = 4*T1

My question: Where does this factor 4 times come from?

Has anyone an idea?

  • I'm rather wary of anything which turns the subjective world of user experience into nice, neat, numbers.
    – PhillipW
    Jul 15 '14 at 8:37

This factor 4 is a rule of thumb. It could have been less (or more) but those who designed the Apdex thought that there would be a high level of consensus in saying that users having to wait more than four times the maximum tolerated usual delay would be frustrated.

Note that the higher the factor, the more underestimated the proportion of frustated users are. Therefore, if you consider 4 a high factor and your conclusion is that your have too many frustrated users, it means that you really have too many frustrated users.

The designers of the Apdex are fully aware that this factor 4 is a convention and they decided to make it configurable to fit with needs where 4 is not considered appropriate, as explained on http://apdex.org/index.php/2010/07/which-apdex-features-can-be-generalized/.

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  • Also have a look at ""Defining The Application Performance Index," by Peter Sevcik, March 2005". There it says "...The above examples indicate ratios of 3:1, 4:1 or 5:1 between the two thresholds, with a prepon- derance of 4. Thus Apdex defines F to be 4 times T, and the three performance zones are defined on a base value of T seconds. ..."
    – enne87
    Jul 15 '14 at 13:42

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