Readability - accounting for common or uncommon words in the text

[HaakonME]

Hi, Matt!

I have imported hundreds of Norwegian EPUB books into Moodle, and I have found that the readability filter is "wrong" too often, i.e. saying the a text is easier than it really is. I believe it can be improved by providing a ratio of common versus uncommon words in a text. Question is - how to best go about it?

A suggestion - if word frequency lists are split by age, i.e. into which words are normally considered common after one, two, three years of reading, then the filter could first do what it already does, i.e. supply a suggestion about number of years of reading - say five - and then it only checks to see the ratio of common versus uncommon words up to five years of reading.