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by Dr Dave Robinson

A column about little things that are deceptively similar, yet decisively different. Read and be prepared.

My international MBA students have just written a series of case-based examinations. One of the cases they had to analyse was 33 pages. Not having English as their first language made the case analysis quite a daunting task for them. Thinking about that reminded me of the term ‘FOG index' – a measure of how difficult a passage is to read. The FOG index was created by Robert Gunning, an American businessman, but I think he must have been a mathematician because what he created was way more complicated than the thing he was trying to measure in the first place, if you know what I mean.

This is how it works: An index is calculated based on the number of words per sentence and the number of complicated words as a percentage of the total number of words. If the FOG index is 10, it means that someone with about ten years of English education will be able to understand the passage. To do the calculation, one must follow the steps below:

  1. Take a complete passage (more than 100 words long).
  2. Find the average sentence length (that is, divide the number of words by the number of sentences).
  3. Count words with three or more syllables (complex words), not including proper nouns (for example, place names).
  4. Add the average sentence length and the percentage of complex words (the percentage, for example 12.43, not the fraction 0.1243)
  5. Multiply the result by 0.4

The formula is represented by the following mathematical equation:

0.4 X {[(No. of complex words / total no. of words) X 100] + [no. of words / no. of sentences]}

To illustrate the principle I took a passage from the Seven Secrets of Synchronicity, which is the book I am currently editing:

“This book will challenge the way you think about life. In the following chapters we will embark on a fascinating journey of discovery. To fully appreciate the Seven Secrets of Synchronicity you will need to unlearn anything you currently assume to be true that doesn't resonate entirely with your spirit, for our truth exists not in that which we acquire by indoctrination, but that which we intuitively feel. The truth connects us unwaveringly to the source of all life, the source of all matter, the source of all that we sense and don't sense. It is, profoundly and unashamedly, Energy.”

The number of sentences is five. The number of words is 100. The number of complex words is 14. Therefore by applying the formula, we can calculate the FOG index to be 13.6.

While the FOG index is a good indication of the complexity of a written passage, it appears to have four limitations. One is that it was ostensibly created for use only with the English language. The second is that not all multi-syllable words are actually difficult. For example, the word ‘anything' is not generally considered to be a difficult word, even though it has three syllables. On the other hand, even some simple words have alternative meanings, and when it comes to the Australian version of English, well any word longer than three syllables gets shortened anyway, such as avo (avocado), servo (service-station) and pollies (politicians). These arguably render the language more difficult, in fact, for the uninitiated to understand, despite lowering its FOG index.

The third limitation is that it isn't at all easy to remember what a FOG index is and how to calculate it. But it is the fourth limitation that has me the most puzzled: Although it is clear you need a level of English to read something with a higher FOG index, given that the purpose of writing something down in the first place is to communicate it to whoever will read it, it would seem more astute to write one's message as simply as possible. That is, with a ‘low FOG index', if it were indeed possible to do so without blurring the meaning. That, however, is a feat that only a few exceptional authors have mastered.

So, I hope my readers will appreciate that after much editing and calculating, I have managed to reduce this article's overall FOG index to 9.597!

By the way, you can apply this technology quite easily whenever you want to. Simply copy and paste any passage of 100 words or more to the following web link and it will calculate the FOG index for you: http://simbon.madpage.com/Fog/

Dr Dave Robinson is a university lecturer, surfer and amateur musician.

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Posted by Dr Dave Robinson
20 Jul 2010

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I enjoyed reading the article knowing that I would never utilise the information. I think you enjoyed the exercise as much as I enjoyed your literary style. God bless ;o)
Rating: 4 / 5
by giulio on 20 Jul 2010

Dave, you have always had a way with words and your article made for interesting reading. I personally think that by the time one had read a passage then applied the formula to break down and analyse it's FOG factor one would actually understand the content and meaning of the passage. So maybe the formula will lead the reader to a better level of comprehension and understanding. the key for me though is to continue reading and thereby learning.
Rating: 4 / 5
by Martin Leverington on 20 Jul 2010

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