5 Reasons Why You Should Stay Away From Readability Formulas

  • Reading time:10 mins read

There is a large number of programs out there that claim to be able to analyze the readability of your content and help you improve the reader experience. In this article, we will cover all of the issues that exist within this type of software and suggest to you a couple of possible and better alternatives.

What Are Readability Formulas And Why Would You Use Them?

As we already mentioned, readability formulas are all applications or programs that analyze written content to improve its readability and the quality of writing. One of the best examples of this type of software would be the Hemingway App. It analyzes the text and detects sentences that are hard to read, opportunities to simplify phrases, and instances where you’re using the passive voice, which can sometimes be tremendously useful.

This type of software is mostly used by writers and bloggers to improve the quality of their content and increase its scannability. Because more readable content of course usually means people sticking around for longer, this improvement can lead to more traffic in the long run, as the readers will be more likely to share that content with someone else.


How Are Readability Formulas Calculated?

Readability formulas account for just a couple of variables when producing their final result and these variables are usually: sentence length, word length, or how well known the words are. These formulas then calculate a final value based on these variables which usually represents the difficulty of reading the text for people of different literacy levels.

Some of the most famous readability formulas are:

  1. Flesch-Kincaid – This formula takes into account the number of words, sentences, and syllables, resulting in a value that corresponds to a U.S. grade level. The results represent the years of education generally required to understand the text.

  2. Flesch Reading Ease – This formula has a very similar equation as the Flesch-Kincaid formula with the only difference being that it doesn’t produce values that correspond to a U.S. grade level. With the Flesch Reading Ease formula the final value is higher if the text is easier to read and goes up to 100, if it’s more difficult to read they become lower and goes to 0.
  3. Dale-Chall Formula – A test that determines the comprehension difficulty of the text by using a list of 3000 words that groups of 4th grade U.S. students could understand, considering any words that aren’t on that list to be difficult. The values for this test go from 4.9 or lower for texts that are easily understood by an average 4th-grade student, all the way to 9.9 for texts that are understood by an average 13th to 15th-grade student.

  4. SMOG Index – Another index that determines the level of education needed for the text to be understood properly, the SMOG index represents an upgraded and more reliable version of the Flesch-Kincaid formula. To calculate it, the number of sentences in a text needs to be greater than 30 and you will need to count the polysyllable words in the text (words with more than 3 syllables).


5 Reasons You Should Avoid Readability Formulas

Even though these formulas can be incredibly useful from time to time for a quick and superficial estimate of your text, the equations on which they are based fail to take into account a large number of variables that constitute the text’s readability. Aside from this, they also have some technical and logical problems which we will cover in this section.


1. These Formulas Don’t Evaluate The Meaning Of Words

Each one of the formulas fails to take into account the complexity of the words that are being used in the text, with the only exception being Dale–Chall which still only gives us a very basic and methodologically improper separation of words into difficult and non-difficult instead of offering a gradient of difficulty.

As you can probably guess, the complexity of the words being used is one of the key factors in determining readability. If we were to use any of our formulas besides Dale–Chall on two texts with similar sentence size and syllables per word, we would get the result that both texts are practically the same in difficulty, even if one of those is a 4th graders essay and the other is a research paper on quantum mechanics.

2. Grade Levels Are Meaningless For Adults

Grade levels are a useful metric for current students as they can help us assess if they are behind or ahead of the curve when it comes to reading capabilities. For adults, on the other hand, grade levels convey very little meaning. What does it mean for an adult to read at a 7th-grade or a 12th-grade level? A 7th grader with that reading level would be normally developed and a fluent reader for his age but an adult that is stuck at the same level would likely be struggling to read and would probably dislike reading in general.

3. Readability Formulas Aren’t Reliable Or Valid

Studies show that using different formulas on the same text oftentimes gives us completely far away results, where they should be concordant as they are measuring the same thing. Even worse than this is the fact that using the same formula on the same text just via different programs, frequently results in completely different values, making these formulas unreliable.

To be valid, these formulas would need to be able to relatively accurately predict the grade level needed to understand a text, however, almost all of them have failed to do so. The only exception here is the SMOG index which yields a 0.985 correlation with the grades of readers who had 100% comprehension of test materials, making it the only valid test out of the ones listed.

4. Improving The Score Doesn’t Equal Improving Readability

Oftentimes focusing on improving the score from the formula can make your text seem more unnatural and thus harder to follow. By trying to improve this specific metric you are neglecting what’s important when it comes to writing, trying to understand the text from the reader’s perspective. These formulas can make the job of improving your text easier by listing the specific problems in it, but things are rarely that simple and you will only achieve slight improvements, if at all.

5. Good Scores Don’t Mean You Have High-Quality Content

Considering that almost all of the formulas don’t take into account the meaning of the words, and even the one that does, only looks at individual words devoid of their context, a good score doesn’t mean anything when it comes to the quality of your content. Theoretically, you could write random, simple words and chain them together in short sentences and you will get a good score, whilst your text is complete gibberish. Instead of focusing on the score, you should always focus on the value that your text is bringing to its readers.


Alternatives To Readability Formulas

As anyone who has ever tried to write a piece of content knows, writing can be difficult and complex if the writer’s goal is to achieve quality. The more reliable and effective ways to achieve a high standard for your content usually take more time and effort but ultimately pay out by allowing you to create an exceptional piece of text that will keep the attention of more readers and lead to more shares for your content.


1. Write For Your Readers

One of the most important things you can do while writing a piece of content is keep your average reader in mind. By staying aware of what your readers do and don’t like you can always correct your writing and stick to the relevant topics whilst keeping a style that thematically suits them. A great way to implement this way of thinking is by creating reader personas, fictional readers that have all the traits that represent their particular reader group. Having a persona will make it easy for you to remember the collection of traits associated with them.

2. Follow Writing Best Practices

There are numerous books out there explaining the theory and practical rules of writing. So many that I won’t even dare to start listing them off. In general, most of these rules are extremely useful and can help you elevate your writing by making it more concise and clear so don’t be afraid to pick up the first book on this topic that you can find as it will probably get the job done. Just don’t be too rigid when it comes to the rules and break away from them whenever you feel like it would benefit your content.

3. Do A Readability Survey

Finally, if you want to asses how your content is being received by the readers, just ask them. The most reliable way to estimate how a piece of content will do with a reader base is to select a decently sized random sample of readers, send them the content and have them fill out a series of questions that are related to the clarity and quality of the content. This of course takes a lot of time and effort and should only be used for content that is of incredibly high importance, but whenever it’s used properly it will also demonstrate powerful results.


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