It often happens that the level rating and the overall rating of a report do not directly match. This is because the ratings of the individual levels (A, AA, AAA) are considered independently of each other. Level AAA is therefore not based on the complete fulfillment of AA test criteria—instead, each level is evaluated separately.
Test Criteria and Their Assignment to Levels
In the WCAG (Web Content Accessibility Guidelines), each test criterion is assigned to a specific level. These levels are A, AA, and AAA.
The evaluation of each individual level only considers the test criteria assigned to that level. This means that only the relevant criteria are included in the rating for each level.
Different Percentages per Level
For example, it is possible that all test criteria for Level AAA are fulfilled, resulting in a 100% rating.
However, for Level AA, only a portion of the criteria may be fulfilled. This can lead to a lower rating, such as 40%, if not all requirements of that level have been met.
Calculation of the Overall Rating
The overall rating is based on a logarithmic calculation, in which all test criteria from the different levels are combined and weighted together.
This means that not only the results of a single level are considered, but also the test criteria from other levels, depending on the selected target conformance, are included in the overall evaluation.
Further Information
More information on how the page rating and overall rating are calculated can be found in the following article:
How is the Page and Overall Score calculated in the Eye-Able Report?