Rating Your Readability

In the 1920s, educators began developing readability formulas as a way of determining suitable reading books for different grade-school levels. In 1944, Robert Gunning developed a simple, quick, and reliable way to measure writing complexity, called the Fog Index^sm scale. The Fog Index^sm score2 represents the approximate number of years of schooling theoretically needed to comprehend, with 90 percent or better accuracy, a passage of writing. Texts with lower scores are easier to read and understand than texts with higher scores. Gunning observed that scores above 12 represented difficult reading, and that 'almost anything [but not everything] can be written within the easy-reading range'. Fog Index ^sm scores are useful, but they do not tell the whole story. They measure neither a text's unity nor its coherence. They simply map your word and sentence length, two key ingredients in determining readability.