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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?
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/.
