The problem with readability scores

August 5, 2010

Readability scores have been available in software such as Microsoft Word for years, and there are several free web-based tools available on the internet too (for example, http://www.online-utility.org/english/readability_test_and_improve.jsp).

To check the readability or (US) grade level of your writing in Word:

  1. Turn on the option to show the readability statistics:
    • Word 2003: Tools > Spelling & Grammar tab, select the Check grammar with spelling check box followed by the Show readability statistics check box, click OK.
    • Word 2007: Microsoft Office button > Word Options button > Proofing. Select the Check grammar with spelling check box followed by the Show readability statistics check box, click OK.
    • Word 2010: File > Options > Proofing. Select the Check grammar with spelling check box followed by the Show readability statistics check box, click OK.
  2. Run the spellchecker. The readability scores (and other statistics) are shown after spell check has finished.

However, I have a big problem with these ‘scores’. The problem I have is that they only seem to take into account individual words in a sentence, the length of the sentence, and the syllables in the individual words. They don’t address how ‘readable’ or understandable the sentence is either as a stand-alone sentence or in context with other sentences around it. These scores look at the raw statistics but don’t seem able to comprehend the words and their order to see if the sentence actually makes sense to a human reader.

Let me give you a simple example.

If my sentence is The cat sat on the mat., I’m going to get a very good readability score. Word’s Flesch Reading Ease score for this sentence is 100.0 and the Flesch-Kincaid Grade Level is 0.0.

If I run this same sentence through the web-based tool I mentioned earlier, I also get a good (though slightly different) result:

So far, so good — you might be wondering why I have a problem with this. Well, the problem is that if I change the words around in this sentence so that the sentence is incomprehensible — e.g. Cat mat the sat the on. or any other variation of these words — I get EXACTLY the same results! Yet I’ve gone from a comprehensible sentence to an incomprehensible one.

While I’ve used a very simple example here, it’s enough to demonstrate why I’m loathe to take the so-called readability statistics at anything more than face value. You could have written a 30,000 word thesis that gets a good ‘readability’ score with one of these indexes, yet it may be totally unreadable. These indexes only look at word length, syllables, sentence length and the like — they don’t assess the order of the words that make up each sentence or the structure of your sentences and paragraphs.

The cat sat on the mat makes sense to a human reader (of the English language); Cat mat the sat the on doesn’t make sense, yet they score exactly the same.

Don’t rely on these scores to tell you how readable your document is. Read it yourself, get someone in your target audience to read it, or get an editor to look it over. Only then will you really find out how ‘readable’ your document really is.

See also: http://plainlanguage.com/newreadability.html

[Links last checked August 2014]


  1. […] The problem with readability scores by Rhonda Bracey […]

  2. […] Rhonda Bracey’s “The problem with readability scores” (https://cybertext.wordpress.com/2010/08/05/the-problem-with-readability-scores/) […]

  3. Having applied readability tests to random pages of the Standards Australia publication AS/NZS 3000.2007 and returned comments that the reader needs to be 27 years of age or older and undertaken post graduate studies, they make sense when the average 18/19 year old aspiring electrician just looks blankly at the pages when trying to read them.
    The standard is known as the “The electricians bible”
    But after completing a B of Ed late in life then I would definitely agree that readability scores are not all they are cracked up to be.

  4. This formula is supposed to evaluate a sentence that means something. Rearranging a sentence like this is simple because it means nothing. In real writing, how would you write meaningless thing and apply the formula?

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