The Fog Index is a tool for estimating the reading difficulty of a technical or expository piece of writing. It is also referred to as a Readability Formula. Applying a formula to a sample of the writing, the average sentence length is calculated. Then the percentage of words with three or more syllables is calculated. The two figures are added together and the sum is multiplied by .4. The result is approximately the "number of years of education (not counting kindergarden) needed to easily and quickly completely understand the writing sample."¹ The details of the formula are given in the source below.

Source:
^1. http://athena.english.vt.edu/~hagedorn/netTW/FogIndex.html (visited March 2001)

Verified by: CM, 3-01

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