Gunning Fog Index
The Gunning Fog Index represents the number of years of formal education that the reader needs in order to understand a particular paragraph or text of English writing on first reading. It is the reader's reading level". It is calculated as follows:
(average number. of words per sentence)
+ (percentage of words that have three or more syllables)
x 0.4 = Gunning Fog Index
The assumption in the formula is that short sentences written in plain English are understood by more persons than long sentences written in complicated language. Therefore, a low number means that more persons will understand the writing than text that has a high number.
Text written for a wide audience normally has a Gunning Fog Index of less than 12. This compares to an Index of 10-15 for technical documentation, 12 for the Atlantic Monthly, 11-12 for the New York Times, 11 for Time magazine, 8 for Ladies' Home Journal, 7 for The Reader's Digest, 7 for True Confessions, and 6 for comic books. The Index for the page entitled "Easy-To-Understand Writing" at this website is 10.0.
An American businessman, Robert Gunning, developed the Index in 1952. The Index is useful to persons who want to ensure that a broad segment of the population will be able to read their writing.
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