When using a specific readability test within the Readability feature in Quality Assurance you may experience different results compared with other readability platforms you have been using. This is not uncommon and this article discusses why a difference in readability score may occur.
Although platforms offer results based on the same readability test using the same algorithm, the level of sophistication behind the logic utilized to collect data to use in the final algorithm can cause a difference in readability score.
Readability platforms can have different criteria for calculating elements used in the final algorithm. For instance: characters, words and sentences. Some may consider dashes, apostrophe, colons etc. as characters, while other may not. Different logic is also utilized in order to count syllables, leading to differing results.
The content extraction performed by Siteimprove, where the boilerplate is removed from each page in order to extract the actual content, is unique to the Siteimprove tool, and can also lead to non-comparable results when compared to other platforms.
Additional resources on Readability: