Automated Readability Index

The Automated Readability Index (ARI) is a readability test designed to gauge the understandability of a text. Like the Flesch-Kincaid Grade Level, Gunning Fog Index, SMOG Index, Fry Readability Formula, and Coleman-Liau Index, it produces an approximate representation of the US grade level needed to comprehend the text.

The formula for calculating the Automated Readability Index is given below:

4.71 \left (\frac{\mbox{characters}}{\mbox{words}} \right) %2B 0.5 \left (\frac{\mbox{words}}{\mbox{sentences}} \right) - 21.43

Characters are the number of letters and numbers.

As a rough guide, US grade level 1 corresponds to ages 6 to 8. Reading level grade 8 corresponds to the typical reading level of a 14 year-old US child. Grade 12, the highest US secondary school grade before college, corresponds to the reading level of a 17 year-old.

Unlike the other indices, the ARI, along with the Coleman-Liau, relies on a factor of characters per word, instead of the usual syllables per word. Although opinion varies on its accuracy as compared to the syllables/word and complex words indices, characters/word is often faster to calculate, as the number of characters is more readily and accurately counted by computer programs than syllables.

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