Flesch-Kincaid readability test

The Flesch–Kincaid readability tests are readability tests designed to indicate how difficult a passage in English is to understand. There are two tests, the Flesch Reading Ease, and the Flesch–Kincaid Grade Level. Although they use the same core measures (word length and sentence length), they have different weighting factors.

The results of the two tests correlate approximately inversely: a text with a comparatively high score on the Reading Ease test should have a lower score on the Grade-Level test. Rudolf Flesch devised the Reading Ease evaluation; somewhat later, he and J. Peter Kincaid developed the Grade Level evaluation for the United States Navy.

"The Flesch–Kincaid" (F–K) reading grade level was developed under contract to the U.S. Navy in 1975 by J. Peter Kincaid and his team. Related U.S. Navy research directed by Kincaid delved into high-tech education (for example, the electronic authoring and delivery of technical information), usefulness of the Flesch–Kincaid readability formula, computer aids for editing tests, illustrated formats to teach procedures, and the Computer Readability Editing System (CRES).

The F–K formula was first used by the Army for assessing the difficulty of technical manuals in 1978 and soon after became a United States Military Standard. Pennsylvania was the first U.S. state to require that automobile insurance policies be written at no higher than a ninth-grade level (14–15 years of age) of reading difficulty, as measured by the F–K formula. This is now a common requirement in many other states and for other legal documents such as insurance policies.

In the Flesch reading-ease test, higher scores indicate material that is easier to read; lower numbers mark passages that are more difficult to read. The formula for the Flesch reading-ease score (FRES) test is

Scores can be interpreted as shown in the table below.

Reader's Digest magazine has a readability index of about 65, Time magazine scores about 52, an average grade six student's written assignment (age of 12) has a readability index of 60–70 (and a reading grade level of six to seven), and the Harvard Law Review has a general readability score in the low 30s. The highest (easiest) readability score possible is around 120 (e.g., every sentence consisting of only two one-syllable words; "The cat sat on the mat." scores 116). The score does not have a theoretical lower bound. It is possible to make the score as low as wanted by arbitrarily including words with many syllables. The sentence "This sentence, taken as a reading passage unto itself, is being used to prove a point." has a readability of 74.1. The sentence "The Australian platypus is seemingly a hybrid of a mammal and reptilian creature." scores 37.5 as it has 24 syllables and 13 words. While Amazon calculates the text of Moby Dick as 57.9, one particularly long sentence about sharks in chapter 64 has a readability score of −146.77. One sentence in the beginning of "Swann's Way", by Marcel Proust, has a score of −515.1. Furthermore, the chemical name for titin, 189,819 characters long, scores a −6,128,472, with 72,443 syllables.

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