Dale–Chall formula
The Dale–Chall formula is one of the ways to predict how difficult text is to read. It is a readability test.[1] The Dale–Chall formula is a one-variable test: it measures the difficulty of the words used. It does not measure the difficulty of the sentence structure (the syntax).
One of the first readability tests, the Dale–Chall formula used a vocabulary list. It counted the number of listed words in a passage, and applied a formula which gave a grade level. It was used to rate textbooks for grade levels in US school districts. In 1995 the authors published an updated word list.[2]
It is easy, in principle, to use a vocabulary list as part of a computer-based readability measure. The list is organised as a look-up table. The percentage of listed words in a passage gives the data for the formula, and the user is presented with a grade level.