Flesch-Kincaid Readability Test

The Flesch/Flesch-Kincaid Readability Tests are readability tests designed to indicate how difficult a reading passage is to understand. There are two tests, the Flesch Reading Ease, and the Flesch-Kincaid Grade Level. Although they supposedly use the same measures, just placed into a different scale, the results of the two tests do not always correlate (a text with a better score on the Reading Ease test over another text may end up with a worse score on the Grade Level test).

Flesch Reading Ease
In the Flesch Reading Ease test higher scores indicate material that is easier to read; lower numbers mark harder-to-read passages. The formula for the Flesch Reading Ease Score (FRES) test is



206.835 - 1.015 \left ( \frac{\mbox{total words}}{\mbox{total sentences}} \right ) - 84.6 \left ( \frac{\mbox{total syllables}}{\mbox{total words}} \right ) $$

where total syllables/total words = average number of syllables per word (ASW) and total words/total sentences = average sentence length (ASL).

As a rule of thumb, scores of 90-100 are considered easily understandable by an average 5th grader. 8th and 9th grade students could easily understand passages with a score of 60-70, and passages with results of 0-30 are best understood by college graduates. Reader's Digest magazine has a readability index of about 65, Time magazine scores about 52, and the Harvard Law Review has a general readability score in the low 30s.

This test has become a U.S. governmental standard. Many government agencies require documents or forms to meet specific readability levels. The U.S. Department of Defense uses the Reading Ease test as the standard test of readability for its documents and forms.

Most states require insurance forms to score 40-50 on the test.

Use of scale is so ubiquitous that it is bundled with the popular word processing programs such as KWord, Lotus® WordPro™ and Microsoft® Word™.

This score is affected significantly more by long words than grade level is.

Flesch-Kincaid Grade Level
An obvious use for readability tests is in the field of education. The "Flesch-Kincaid Grade Level Formula" translates the 0-100 score to a U.S. grade level, making it easier for teachers, parents, librarians, and others to judge the readability level of various books and texts. It can also mean the number of years of education required to understand this text, relevant when the formula results in a number greater than 12. The grade level is calculated with the following formula:



0.39 \left ( \frac{\mbox{total words}}{\mbox{total sentences}} \right ) + 11.8 \left ( \frac{\mbox{total syllables}}{\mbox{total words}} \right ) - 15.59 $$

The result is a number that corresponds with a grade level. For example, a score of 6.1 would indicate that the text is understandable by an average student in 6th grade.

History
An early form of the test was developed by Dr. Rudolf Flesch (author of Why Johnny Can't Read) in the 1940s. J.P. Kincaid modified the test based on work with Navy inductees' understanding of their training manuals. They jointly published their work on readability levels in 1975.