SMOG (Simple Measure Of Gobbledygook)

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SMOG (Simple Measure Of Gobbledygook) is a readability formula that estimates the years of education needed to understand a piece of writing. SMOG is widely used, particularly for checking health messages. The precise SMOG formula yields an outstandingly high 0.985 correlation with the grades of readers who had 100% comprehension of test materials.

SMOG was published by G. Harry McLaughlin in 1969[1] as a more accurate and more easily calculated substitute for the Gunning-Fog_Index. To make calculating a text’s readability as simple as possible an approximate formula was also given — count the words of 3 or more syllables in 3 10-sentence samples, estimate the count’s square root (from the nearest perfect square), and add 3.

[edit] Formula

To calculate SMOG

Count a number of sentences (at least: 10 from the start of a text, 10 from the middle, and 10 from the end).
In those sentences count the polysyllables (words of 3 or more syllables).
Apply this formula:

$1.0430 \ \sqrt{\mbox{number of polysyllables} \times \left ( \frac{30}{\mbox{number of sentences}} \right )} \ + 3.1291$

which approximates to

$\sqrt{\mbox{number of polysyllables} \times \left ( \frac{30}{\mbox{number of sentences}} \right )} \ + 3$