Fog: a cloudlike mass
or layer of
minute water droplets
or ice crystals
near the surface
of the earth,
appreciably reducing visibility; something that obscures and confuses a situation
or someone's thought processes.
The second part of that definition certainly applies to
writing. No one likes to read prose so difficult that they end up in a fog,
with the subject so obscure that they don’t know what to think. From this came
the concept of the Fog Index. And this entry is for the mathematicians.
The Fog Index was created as a way of calculating just how
difficult a piece of writing is to read. It has serious limitations, but
looking at the formula is certainly illuminating, even for non-mathematicians
(like me—show me numbers, and I run the other direction).
The formula follows:
0.4 [(words/sentences)
+ 100(complex words/words)]
Or as I prefer it:
Fog
Index = 0.4(Average Sentence Length + %Hard Words)
Hard words are words three syllables long or more, not
counting proper names. What you get is a number that corresponds to the number
of years of school required to understand a piece of writing. So a Fog Index of
12 means someone with a high school degree should be able to understand it
easily.
Most word processors will calculate a reading scale of some
sort, but I prefer the Fog Index because of what you can see in the formula. What
makes the Fog Index go higher? Longer sentences and hard words. I am editing a
paper right now with a high Fog Index. It sits right at 26. That’s not just
high school, but college, both master’s and PhD, and a post doc.
As a general indication of readability, the Fog Index works
pretty well. Short sentences and short words (along with short paragraphs) are
easier to read than long sentences and long words (and long paragraphs).
This formula does have drawbacks. First of all, not all long
words are hard words. And not all readers find the same words hard. Moreover,
not all long sentences are difficult to read; that depends entirely on the
writer. The Fog Index doesn’t solve all the problems of writing that is too
obscure to read, but it certainly provides a little insight.
I thought about providing examples. Instead, I provide a website:
Have fun!
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