Coleman-Liau Index Readability

Introduction

Unlike other readability tests, the Coleman-Liau Index does not subscribe to formulas cemented in syllables. Instead, it takes into account how long words are by the number of letters. Though it differs from the others, the Coleman-Liau Readability Index is still one of the most commonly used today.

It was developed by a pair of linguists, Meri Coleman and T.L. Liau, in 1975 to assess the readability of the textbooks used in public schools in the United States. The idea behind the formula is because Coleman and Liau both think that syllable-counting lacks accuracy and is very time-consuming.

Description

Instead of manually counting the syllables, Coleman and Liau offer users the chance to use a machine to count the letters per word in a text. This is more accurate than a machine counting syllables as syllabic count might not necessarily mean easy understanding.

Take, for example, the words ‘going’ and ‘boing.’ Both have two syllables, but ‘boing’ isn’t as common as ‘going.’ Machine interpretations can be challenging to assess and can be prone to error.

With the Coleman-Liau Index, you can get the grade level a reader requires to have to understand a text without syllable counting. It is also easy to interpret the Coleman-Liau readability score since it directly shows the grade level needed.

An index score of 6, for example, states that your text can be understood by an audience of 6th graders and older using the US schooling system. If you are writing for the general public, it’s best to aim for an index score of 8 to 10 since 8th to 10th Grade uses conversational English the most.

Formula

To get the most accurate result in the Coleman-Liau Index, you will need to get a sample passage of at least 300 words.

The formula you need to use is pretty straightforward. Read below:
CLI = 0.0588L – 0.296S – 15.8

Where,

CLI = Coleman-Liau Index Score

L = Average number of letters per 100 words

S = Average number of sentences per 100 words

Grade Conversion

Below is a simple conversion table that shows the possible score you get in the Coleman-Liau Index and what they can mean.

Index Score School Level Comprehension
5 & below 5th Grade and below Very easy to read
6 6th Grade Easy to read
7 7th Grade Fairly easy to read
7-10 8th, 9th & 10th Grade Conversational English
11-12 11th & 12th Grade Fairly difficult to read
13-16 College Difficult to read
17+ Professional Extremely difficult to read

Uses

The first use for the Coleman-Liau Index is for educational purposes. As such, it is still a good readability test to use for textbooks and other teaching tools. But its use today has broadened and can be implemented in different industries.

Aside from schools, medical documents are also being subjected to the Coleman-Liau Readability Test. You can also use it to compare texts in other Western-European languages like German or Spanish.

However, it’s a good idea to remember that the Coleman-Liau Index was formulated for the English language. Therefore, it can be used as a marker or comparative test for two texts in one non-English language. But the grade level you get is rendered meaningless if the text is not in English.

How to Improve Score

Like many other readability tests, improving your score in the Coleman-Liau Index is reasonably straightforward. All you need to do is write simply and use common words. Words that are spoken in daily conversations are more comprehensible to the average person. If you’re reaching for a general audience, the simpler the words you use, the better.

Further Readings

Wikipedia

Coleman-Liau Index

The Coleman-Liau Index is:

See Grade Conversion Table to interpret the score.