Apdex is a simple scoring system which is an open standard developed by an alliance of companies as a standard method for reporting and comparing the performance of applications. WebTuna has calculated Apdex for some time and exposed it through our REST API but today we have added visibility of the Apdex score into the WebTuna Performance screen.
Apdex in WebTuna
WebTuna calculates the Apdex score for every single page or AJAX request that is captured and categorises it into one of the 3 categories (Satisfied, Tolerating or Frustrated). That measurement is then used to calculate the overall score using the formula below.
How does Apdex work?
Apdex defines three performance zones:
- Satisfied Response times that are fast enough to satisfy the user, who is therefore able to concentrate fully on the work at hand, with minimal negative impact on his/her thought process.
- Tolerating Responses in the tolerating zone are longer than those of the satisfied zone, exceeding the threshold at which the user notices how long it takes to interact with the system, and potentially impairing the user’s productivity. Application responses in this zone are less than ideal but don’t by themselves threaten the usability of the application.
- Frustrated As response times increase, at some threshold the user becomes unhappy with slow performance entering the frustrated zone. With response times in the frustrated zone, a casual user is likely to abandon a course of action and a production user is likely to cancel a Task.
The three zones are defined by two thresholds: T and F, in seconds, as follows.
- Satisfied Zone = zero to T.
- Tolerating Zone = Greater than T to F.
- Frustrated Zone = Greater than F The value of F is four times the value T.
For example, if users perceive response time as tolerable beginning at 4 seconds then they will be frustrated at greater than 16 seconds.
In WebTuna T is defined by the target page load time for the site which is defined under Domain Target Page Load Time on the Admin screen.
Apdex score calculation
Apdex score is calculated as:
To achieve the optimal Apdex value of 1.00, all users must experience satisfactory performance. If some users see tolerating or frustrating performance, then the index rapidly dips below 1.00. For example, if 80% of users are satisfied and 10% are tolerating, while the remaining 10% are frustrated, the index is 0.85.