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The Fog Index

Posted on Tuesday, September 29, 2015 at 11:10 PM

Assessing the readability of a WashingtonPost.com excerpt.

This month, we're analyzing the Fog Index of an excerpt from a September 28 WashingtonPost.com article ("NASA Confirms the Best-Ever Evidence for Water on Mars" by Rachel Feltman). Here's the sample, with longer words in italics for reference:

"The study builds on research from April, when scientists using data from the Curiosity rover noted that the planet had the seasonal potential for liquid water. We know that because of the extremely low pressure on Mars, water has a boiling point of just a few degrees Celsius, after which it evaporates. The April study noted the presence of perchlorates -- a kind of salt -- which could make the boiling point of Mars's water much higher, theoretically allowing it to remain liquid. They posited that the planet's temperature would be right for liquid, perchlorate-filled water to form every day during winter and spring."

--Word count: 102 words
--Average sentence length: 26 words (26, 26, 29, 21)
--Words with 3+ syllables: 8 percent (8/102 words)
--Fog Index: (26+8)*.4 = 13 (13.6, no rounding)

The number of longer words is quite low for a sample of this size. However, we have just over 100 words split into just four sentences. Let's see if we can pare down our average sentence length to cut at least 2 points from our Fog score.

"The study builds on research from April, when scientists using data from the Curiosity rover noted that the planet had the seasonal potential for liquid water. We know that because of the extremely low pressure on Mars, water has a boiling point of just a few degrees Celsius. After that point it evaporates. The April study noted the presence of perchlorates, a kind of salt that could make the boiling point of Mars's water much higher. Theoretically, this would allow it to remain liquid. The experts posited that the planet's temperature would be right for liquid, perchlorate-filled water to form every day during winter and spring."

--Word count: 106 words
--Average sentence length: 18 words (26, 22, 5, 23, 8, 22)
--Words with 3+ syllables: 8 percent (8/106 words)
--Fog Index: (18+8)*.4 = 10 (10.4, no rounding)

We didn't have to do much to this sample to improve the Fog score. With a few very minor syntax tweaks, we turned four sentences into six. This was all the editing we needed to cut 3 points from the original sample's Fog Index, bringing us well within ideal range (i.e., below 12).

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