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The clarity index

Some writing problems do not lend themselves to a quick-screen edit. A second tool, the clarity index, pinpoints two other major reasons why writing that arrives on the desk is often confusing and difficult to read.

a. Long words and long sentences make writing difficult to read. Such writing does not meet the new standards of Army writing. The clarity index provides a yardstick to measure how readable writing is. If you suspect that writing is not effective, this yardstick is helpful to quantify the problem.

b. The clarity index is based on word and sentence length. Select­ing a sample of 200 words or less, use the formula below.

  1. Count the number of sentences.
  2. Count the number of words.
  3. Divide the number of words by the number of sentences to get the average sentence length. (The target average is 15 words per sentence.)
  4. Count the number of words that have three syllables or more.
  5. Divide the number of long words by the total of words to determine the percentage of long words. (The target is 15 percent.)
  6. Add the average sentence length to the percentage of long words.
  7. The sum is the clarity index. (The target is 30.)

c. If a writer eliminates long words and long sentences without changing meaning, writing becomes clearer. The writer is not pro­ducing simplistic papers or insulting the reader’s intelligence. In­stead, time-savings and understanding increase.

d. Use the clarity index once to quantify the density of a piece of writing for subordinates. Then have them periodically monitor their own writing.

e. Use the following Rules of thumb for the clarity index:

  1. Below 20, writing is too abrupt.
  2. Over 40, writing is difficult to understand.
  3. Aim for an index of 30.

From Army Pamphlet 600-67, Effective Writing for Army Leaders, section 4-3