Tip 6. Be Cautious About Using Readability Formulas

There are several dozen readability formulas, including the Fry formula, SMOG, and Flesch tests (Flesch-Kincaid and Flesch Reading Ease). You can use the formulas to score text by hand or use computerized versions that are built into word processing programs or other software. Results from these formulas are often given as a grade level, such as “4th grade” or “12th grade.”

Why Be Cautious About Formulas?

Since many people are unaware of the narrow and mechanical focus of these formulas, the grade level scores from these formulas are often interpreted and used in ways that go well beyond what they measure. If you are thinking of using a readability formula to assess the text you have written for your quality report, here are some things to know:

  • The grade level score from a readability formula is based on the average length of the words and sentences. Though the formulas vary, they generally assume that longer words are harder words and longer sentences are harder sentences. They can’t tell you whether the words you are using are familiar to your readers or whether the sentences you have written are clear and cohesive.
  • The formulas do not measure comprehension or reading ease. Readability formulas completely ignore most factors that contribute to ease of reading and comprehension, including the active role of the reader.[1][2] A grade-level score tells you nothing about whether your quality report will attract and hold people’s attention, whether the content is organized in an effective way, or whether people will be able to understand and use it. This means that a grade level score, by itself, is not a good way to judge the overall suitability of your report.
  • There are serious measurement issues. The grade-level scores for the same text can differ by several grade levels, depending on which formula is used. Also, if you use a computerized readability formula (such as the ones that are built into some word processing programs), you must prepare the text first to avoid misleading results. This includes removing embedded punctuation and text that is not in full sentences, such as headings and bulleted points.

Using the Formulas as a Diagnostic Tool

Although readability formulas are not appropriate for making an overall assessment of the ease of comprehension or use of your report, they can be a good tool for alerting you that your text is too difficult and you need to make revisions.

To determine whether your text is too difficult for your intended readers, start by estimating your audience’s reading skills. Here are two ways:

  • Years of education. Research has found that a person’s reading level is usually 3 to 5 years below the highest grade that person has completed. If you know how much schooling the typical member of your audience has, you can estimate the average reading level.
  • National Adult Literacy Survey. The National Adult Literacy Survey (NALS) shows literacy levels for people of different ages, races/ethnicities, and health status.[3] If you know the demographics of your audience, you can use data from this survey to estimate the average reading level.

Next, consider the grade level score for your report. The scores produced by readability formulas, such as “grade 9.4,” sound more precise than they really are. Readability experts often advise that the scores be interpreted in a more general way. For example, for an audience of consumers:

  • Material written at the fourth- to sixth-grade level is considered easy to read.
  • Seventh- to ninth-grade materials are considered to be of average difficulty.
  • Anything written at a 10th grade level or above is considered difficult.

Now compare the score for your text with your estimate of the average reading skills of your audience. If the grade-level score seems too high for your audience (or if the score is 10th grade or higher), take a close look at your words and sentences. The long words (generally, words of three or more syllables) and long sentences are giving your text a high grade-level score.

  • Circle the long words and consider whether they are likely to be familiar to your readers.
  • Circle any shorter words you think might be difficult for your readers.
  • Circle the lengthy sentences and consider whether they are likely to be hard for your readers to understand.
  • Circle any shorter sentences that have complex syntax or seem like they might be hard for people to understand.

Can you simplify these words and sentences? Can you clarify the meaning? If you can, it will make your text easier for readers to understand and use.

Learn more about the appropriate use of readability formulas in Using readability formulas: a cautionary note, in the Toolkit for Making Written Material Clear and Effective (forthcoming), Section 4, Part 7. Written by Jeanne McGee for the Centers for Medicare & Medicaid Services. Available at http://www.cms.gov/Outreach-and-Education/Outreach/WrittenMaterialsToolkit/index.html?redirect=/WrittenMaterialsToolkit/09_ToolkitPart07.asp#TopOfPage.

Remember that many important things besides length of words and sentences contribute to good writing. For help in making edits to improve your text, use the tips in this guide and the suggestions in Guidelines and Other Resources To Fine-tune Your Writing.


[1] Redish J. Readability formulas have even more limitations than Klare discusses. ACM J Compu Doc 2000 August 24(3):132-7.
[2] Redish JC, Selzer J. The place of readability formulas in technical communication. Tech Commun Fourth Quarter 1985:46-52.
[3] National Adult Literacy Survey: Key Findings of the National Assessment of Adult Literacy. Available at http://nces.ed.gov/naal/kf_demographics.asp.


Also in "Tips on Writing a Quality Report"

Page last reviewed May 2015
Page originally created February 2015
Internet Citation: Tip 6. Be Cautious About Using Readability Formulas. Content last reviewed May 2015. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/professionals/quality-patient-safety/talkingquality/resources/writing/tip6.html