You want to make your documents easy to understand. You want people to follow instructions, make decisions or send information to you. So you want to use plain language.
You’ve possibly been told about reading levels or grade levels. And you’ve probably been encouraged to use a readability formula (such as the one in Word) to get your text down to a certain grade level. Sometimes running a document through a readability tool is all people do to flag plain language issues.
Plain language experts say these tools are actually not useful. And they could even undermine all the other proven techniques you can use.
Wait! What? Is this new?
The idea that readability formulas are problematic goes back a long way. As early as the 1980s, people were researching it and talking about it.
“By the mid-1980s, there was a widespread sense that plain-language advocates had shifted priorities from readability to usability.”
“Research tells us that most readability formulas are outdated methods for assessing text quality.”
– Dr. Karen Schriver
Readability formulas are ineffective and counterproductive
Dr. Schriver described some research on this from Richard Kern, which was published in 1980 (so experts have known about this for a long time).
Kern’s research highlighted important problems with readability scores:
- (1) Readability formulas cannot match material to readers at targeted grade levels.
- (2) Rewriting to lower the reading-grade level score does not increase comprehension.
- (3) Requiring that text be written to satisfy a targeted reading-grade level focuses attention on meeting the score requirement rather than on organizing the material to meet the reader’s information needs.
Dr. Schriver also described how people learn to write simply to get a better score.
But this does not increase reader comprehension.
Readability formulas don’t measure the right things
“Most of what makes a document usable is not included in readability formulas.”
– Dr. Ginny Redish
Dr. Redish describes why the formulas don’t measure the right things.
- They were not created for technical documents.
- They assume that short words are always the better words.
- They don’t work with many documented features of plain language.
Let’s look at the last two in that list because they are easy to follow.
Readability formulas assume that short words are always the better words
Plain language requires you to write for your audience’s needs. So what qualifies as plain writing depends on who the audience is. The goal is to pick words that are familiar to the reader, not to use short words all the time.
Sometimes short words are harder to understand because they are abstract (ennui, writ) or carry a lot of historical meaning (fez, nadir). But a formula will score them as easy words.
“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.”
– Agency for Healthcare Research and Quality, US Department of Health and Human Services
Readability formulas don’t work with many documented features of plain language
Bulleted lists are known to be very helpful to readers (if used to properly chunk information), but readability formulas score such text as harder to read.
“Readability formulas assume that you are writing prose paragraphs. They count sentence length by going from period to period. If you use bulleted lists to chunk your material and lay your text out with white space, readability formulas will say you have long sentences. Yet, usability studies have consistently shown the value of lists and white space as aids to locating and understanding information.”
– Dr. Redish
You can see a demonstration of this point with an example in one of Dr. Redish’s publications.
Dr. Redish also notes these critical techniques that readability formulas do not measure:
- determining the right content for readers
- organizing the material for readers
- using meaningful headings and other tools to guide readers
In her paper (written with Caroline Jarrett), she explains why improving readability scores doesn’t usually correlate with improving comprehension. In fact, she gives a specific example where the version with a readability score that indicated it was easier to understand was actually less understandable to the people who needed to read the document.
The ISO plain language standard excludes such formulas
An international working group made up of experts from 25 countries wrote the ISO plain language standard (published in June 2023). Between them, these experts speak 19 languages and work in a wide range of roles and organizations. Many of these experts have been doing research on plain language for decades.
This group of experts all agreed with this wording in the standard:
“Plain language ensures readers can find what they need, understand it, and use it. Thus, plain language focuses on how successfully readers can use the document rather than on mechanical measures such as readability formulas.”
And there is no mention of readability formulas in the standard besides that explicit exclusion of them.
What’s in the standard?
“Plain language” is defined as follows in the standard:
Communication in which wording, structure and design are so clear that intended readers can easily
- find what they need,
- understand what they find, and
- use that information.
The four principles in the standard give details on what methods can be used to write a plain language document:
- Readers get what they need (relevant)
- Readers can easily find what they need (findable)
- Readers can easily understand what they find (understandable)
- Readers can easily use the information (usable)
Where does this leave us on using readability formulas for plain language?
We can see then that since the early 1980s researchers have agreed that readability formulas focus only on a very small part of what makes a communication plain. It’s also clear that the international experts who worked on the ISO standard for plain language decided not to support using readability formulas for assessing the clarity of texts for audiences around the world. You should reconsider your use of the formulas and instead evaluate text quality by testing your communications with intended readers.
View sources
- Note that Dr. Redish and Dr. Schriver endorse this summary of their research (personal communication to Gael Spivak). And Dr. Schriver contributed the closing paragraph.
- Agency for Healthcare Research and Quality, United States Department of Health and Human Services. “Tip 6. Use Caution With Readability Formulas for Quality Reports.”
- ISO standard 24495-1 Plain language — Part 1: Governing principles and guidelines, quoted with permission from Committee Manager: Mr. Changqing Zhou of ISO Technical Committee 37: Language and terminology.
- Jarrett, Caroline, and Ginny Redish. “Readability Formulas: 7 Reasons to Avoid Them and What to Do Instead.” UXmatters, July 29, 2019.
- Redish, Ginny. “Readability formulas have even more limitations than Klare discusses.” (PDF) ACM Journal of Computer Documentation 24(3), August 2000, 132–137.
- Schriver, Karen. "Evaluating Text Quality: The Continuum from Text-Focused to Reader-Focused Methods." (PDF) IEEE Transactions on Professional Communication 32(4), (1989): 238–55.
- Schriver, Karen. “Readability Formulas in the New Millennium: What’s the Use?” (PDF) ACM Journal of Computer Documentation, 24(3), August 2000, 138–140.
- Schriver, Karen. “Plain Language in the US Gains Momentum: 1940 – 2015.” (PDF) IEEE Transactions on Professional Communication, 60(4), 2017, 343–383.
