Readability Index (LIX) is a measure of how advanced a text is. Carl-Hugo Bjornsson introduced the method 1968. The LIX number is calculated using a system where the number of long words and the number of sentences in the text are weighed with the number of words in the whole text.
LIX = W / S + 100 * L / W
W = number of words in the texts
S = number of sentences in the text
L = number of long words (longer than 6 letters)
The formula can thereby be read as "number of words per sentence added with the percentage of long words in the text".
From the scale below it is possible to evaluate the readability of a text:
| LIX number | Kind of text |
|---|---|
| Below 25 | Childrens books |
| 25 to 30 | Simple texts |
| 30 to 40 | Normal texts / fiction |
| 40 to 50 | Fact texts, for example Wikipedia |
| 50 to 60 | Fact books / white papers |
| Above 60 | Difficult facts / research / thesis |