What is the FOG INDEX?

We all know that some things are easier to read than others. A primary school text book on butterflies, for example, compared to one written for university students – which has to be a good thing, since not everybody has the same reading level, regardless of their intellect, culture or education level. 

Yet while somebody who has the ability to read long, complicated sentences can read something simpler, the same cannot be said of those who are less capable. A situation that can cause no end of difficulties if writers write without taking into account who the readers of that work will be.
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' For w
hen you want
each reader to believe you're writing only
for them.' 

Elizabeth Bezant
This is something that Robert Gunning, an American textbook publisher, was all too well aware of. One of his more publicised beliefs was that newspapers and many business documents were unnecessarily complicated, or put another way, ‘full of fog.’

So, in 1944, he founded the first readability consulting firm, through which he researched, tested and worked with many popular publications, newspapers, writers and editors. In 1952 he then created the Fog Index, a mathematical calculation allowing every writer to calculate the ideal reading level needed for their writing. This was then published in his book, The Technique of Clear Writing.

While the Fog Index has undergone some changes over the years, and still can’t be relied on for a consistently perfect indication of the reading level of a piece of writing, it certainly offers helpful insights and feedback.

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