FOG Index

FOG Index

We all now how important it is to write for our market, right? And we all know that one of the major ways to do this is to write in a style that the reader can understand. But how do we know that what we're writing is at the right reading level for our audience?

For many years, I‘ve been teaching that if you want to write for the general public be aware that most people have, or enjoy reading at, the reading level of a 12 to 15 year old. In theory this means avoiding many long syllabled words, unusual words, or long and awkward sentences.

But what if, as a writer, you want to be more specific information than that? That’s when standards, such as the FOG Index (suggested to have an 80% correct outcome) have to be considered. There are a variety of other systems, but this one seems to work as well as the next and is my favourite.

The FOG Index was devised by Robert Gunning in 1952. And whilst he was an American it would also appear that he was, for some time, Professor of English at Oxford University in England, the oldest university in any English speaking country.
In 1944, Gunning formed his own readability consultancy. His goal with this company was to make newspapers more readable. Previous to this most books and newspapers had been written with limited concern as to the readers’ abilities. If you look back to children’s books around this time the variation between them and adult books is more on topic than vocabulary.
The calculation used to reach the FOG Index on any work is:

1) Take a 100 word extract (ending at a full stop).
2) Count the number of sentences in this section.
3) Divide 100 by the number of sentences. This will show the average sentence length (ASL).
4) Count the number of long words (NLW), those that have 3 syllables or more.
5) Add the ASL and NLW then multiply by 0.4. This will equal the FOG Index.

To give you an idea of the FOG Index on different publications Reader’s Digest is 8 - 9, Time, The Wall Street Journal are 11, and The Bible, Mark Twain and Shakespeare are about 6.

Now whilst it would not be wise to measure every sentence you write by this calculation, or any like it, the formula can help give you an idea of how appropriate their writing is for your reader.

So here is the guideline to go by

7 - 8 = general populus
10 = average 15 year old
11 - 13 = college student
14 - 16 = university student
over 18 = too difficult for newspapers

And just in case you are wondering, from the excerpt I took of this article it rates at 9.2 on the index.
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