Automated Readability Index

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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, its output is an approximate representation of the U.S. grade level needed to comprehend the text.

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 easier to calculate, as the number of characters is more readily and accurately counted by computer programs than syllables.

[edit] Formula

To calculate the Automated Readability Index:

  1. Divide the number of characters by the number of words, and multiply by 4.71.
  2. Divide the number of words by the number of sentences, and multiply by 0.5.
  3. Add #1 and #2 together, and subtract 21.43.
ARI = 4.71 \left ( \frac{\mbox{characters}}{\mbox{words}} \right ) + 0.5 \left ( \frac{\mbox{words}}{\mbox{sentence}} \right ) - 21.43

The output approximates the minimum grade level needed to comprehend the text. A score of 8.2, for instance, should easily be understood by the average 14-year-old.

[edit] External links