A concern of any good author is the readability of his/her text with primary consideration given to the intended audience. If the readability is too low, the author risks the esoteric; if too high, the mundane. A means to objectively calculate a readability score allows not only the evaluation of a single passage, but also the ability to compare passages using a definite scale. The Flesch Reading Ease Test was developed by Rudolf Flesch in the mid-twentieth century to fill this need. However, the formula is complicated and largely based on one individual’s assumptions. The test is included in several word processing packages and continues to be used frequently even though its derivation is largely unknown to its users.
Rudolf Flesch (1911-1986) was an author and writing consultant most remembered for his 1955 book “Why Johnny Can’t Read.” Raised in Austria, he studied law and later moved to the United States and earned a PhD from Columbia University. The author of many books on teaching English, he quickly established himself as an expert in the field. In a 1949 book titled “The Art of Readable English”, he laid down the formula for calculating readability. The formula, which relies on statistics published by another author, is based on the trend of decreasing sentence length since the 16 century.
The Flesch Reading Ease Test is calculated by the following method: The average sentence length is multiplied by 1.015 and the average number of syllables is multiplied by 0.846. These two products are subtracted and then that value is subtracted from 206.8 resulting in a score ranging from 0 to 100. This formula is depicted below:
206.8 – 1.015 (total words/total sentences) – 84.6 (total syllables/total words)
A score of 100 represents the easiest to read text and a score of 0 represents the most difficult to read text. Scores ranging from 60 to 70 are considered to be plain English and, therefore, readable by the average literate reader. To translate the Flesch Reading Ease Test to a grade level, the Flesch-Kincaid formula is useful. The formula takes the average words length and multiplies it by 0.39 and the average number of syllables and multiplies it by 11.8. These products are added together and the result is finally subtracted by 15.59. This formula is depicted below:
0.39 (total words/total sentences) + 11.8 (total syllables/total words) – 15.59
A score of about 65 correlates with the 8th to 9th grade level and a score of about 55 indicates a 10th to 12th grade level. Scores between 0 and 30 represent college graduate level readability.
A competing readability scale developed by Robert Gunning called the Fog index, considers the percentage of “foggy” words or words with 3 syllables or more. Otherwise, this index is similar in aim and approach to the Flesch method.
One problem with readability formulae is that they ignore the actual vocabulary used in writing. For example, the two words governmental and acephalous both have 4 syllables and would contribute to the syllable portion of the Flesch Readability Scale equally. However, governmental contains 12 letters thereby contributing to a lower score than the 10 letters in acephalous. The problem identified here is that the test assumes that there is a strong negative correlation between word length and a word’s readability. Clearly, acephalous is a word rarely found in written English whereas governmental is much more common.
Readability statistics available may provide a quick solution to evaluating the audiences most likely to be able to read your text, but there are some caveats. An ideal scale would take into account more than just simple calculations of words and syllables. Authors must also consider the lexicon used in the text given the example cited above. The lesson learned: For a one-click evaluation, readability statistics do provide a quick glimpse into readability but any good author knows not to rely on this method exclusively.