Different mathematical methods have been developed to formally determine the readability of a text. Two criteria that can be determined quickly using appropriate analysis tools are, for example, the length of the sentence and the word length. These and other factors are related to each other by mathematical formulas and the so-called readability index is calculated from them. This readability index does not replace human judgment, but it does provide an indication as to whether the text meets the formal criteria for good readability.
The readability of texts is currently being discussed, mainly in the area of SEO. This aspect, however, has been important for a long time – as long as texts have been around – since people want them to be as easy to understand as possible. The most popular readability index, the Flesch Reading Ease Index (in short: FRE Index), is older than the internet. It was developed by the author Rudolf Flesch, who researched the topic of usability in the 1940s and 1950s. Another model for evaluating text comprehensibility is the Hamburg Concept of Comprehensibility. A Hamburg research group developed this in the 1960s and 1970s to simplify officialese. The purpose of this simplification was to reproduce information in such a way that all population groups could understand it equally.
There are many other models in addition to these two, meaning that the readability index is not the same in every case. The individual measuring methods create different criteria, are developed for different languages, and sometimes have very special target groups or text forms in their sights. When it comes to journalistic texts, however, the objectivity criteria must be weighted higher than it would be for a marketing text.