Text leveling is commonly used to rank the reading ease of texts in areas where reading difficulties are easy to identify, such as books for young children.
At higher levels, ranking reading ease becomes more difficult, as individual difficulties become harder to identify.
Kitson’s work showed that each type of reader bought and read their own type of text.
On reading two newspapers and two magazines, he found that short sentence length and short word length were the best contributors to reading ease.
In 1921, Thorndike published Teachers Word Book, which contained the frequencies of 10,000 words.
It made it easier for teachers to choose books that matched class reading skills. They were concerned that junior high school science textbooks had so many technical words.
In readers with average or poor reading comprehension, raising the readability level of a text from mediocre to good can make the difference between success and failure of its communication goals.
Readability exists in both natural language and programming languages though in different forms.
Higher readability eases reading effort and speed for any reader, but it is especially important for those who do not have high reading comprehension.
They validated it by using an outside criterion, and correlated .845 with test scores of students who read and liked the criterion books. It was a two-year study of adult reading interests.