Burkey Belser’s Communication Index

By Nirmaldasan



— Appeared in the proceedings of the 4th national conference on the theme ‘Redefining the Role of Language in Higher Education’, conducted by the Department of English & Foreign Languages, SRM University, in association with Regional Institute of English in South India on 12th and 13th March 2009. —


In the communication process, linguistic skills play a key role in shaping the message.  But effective communication depends not just on grammar and style. Robert Gunning, creator of the popular readability formula Fog Index, had extensively researched business writing and found that only in a few samples did grammatical mistakes interfere with communication (How To Take The Fog Out Of Writing 48). Rudolph Flesch derived two formulae in 1948: one for predicting reading ease; and the other for predicting human interest. While Flesch’s first formula Reading Ease looks at sentence-length and word-length, the second goes beyond language itself. Here is his Human Interest (HI) Formula: HI = 3.635pw + 0.314ps. Substituting the values of pw (percentage of personal words) and ps (percentage of personal sentences) in the formula, we get a score on a 100-point scale; the higher the score, the greater the human interest (‘A New Readability Yardstick’ 231). 


Flesch gave clear rules for counting personal words and personal sentences. But the presence of the decimal points in the formula may explain why it is seldom used today. However, his formula paved the way for the identification of more factors of effective communication.


Four factors

In 2006, Burkey Belser identified four factors that affect communication and derived the Communication Index Formula to arm communicators with a quantitative tool that would indicate whether communication has been effective. In an online article, he explained the use of his formula and showed why millions read Peanuts and why technical journals are not on the newsstand (‘The Communication Index’, June 2006).


These are the four factors: 1. Difficulty of the subject; 2. Difficulty of the presentation; 3. Motivation of the audience; and 4. Expertise of the audience. Each factor is assigned a relative value on a scale of 1 to 10. 


Communicators have least control over the expertise of the audience. However, if they know the audience’s knowledge levels, it becomes easier to choose an appropriate subject and presentation. Even the least motivated audience may be easily persuaded to look at an exciting presentation. The presentation holds the key to effective communication and is shaped by an understanding of the other factors. Burkey’s law states that even the most motivated reader can be defeated thanks to the difficulty of the subject as well as the difficulty of the presentation. Here are his corollaries: 1. As the difficulty of the subject matter increases, the probability that material will be read, no matter how motivated the reader, decreases; and 2. As the difficulty of the presentation increases, the probability that material will be read, no matter how motivated the reader, decreases.   


Communication Index Formula

The Communication Index (CI) = (S x P) / (M x E)


Step I: Assign values to subject difficulty (S), presentation difficulty (P), motivation of the audience (M) and the expertise of the audience (E). Belser says that even rough measures provide an accurate CI.


Step II: Calculate the numerator by multiplying S and P.


Step III: Calculate the denominator by multiplying M and E.


Step IV: Divide the numerator by the denominator.


Belser writes: “The best communication occurs between .01 and 1. Communication increases in difficulty from 1 to 10. And it starts to fail utterly at higher numbers.”


When the variables take extreme values of 1 and 10, the CI takes the following values:


(10 x 10) / (10 x 10) = 100 / 100 = 1

(1 x 1) / (1 x 1) = 1 / 1 = 1

(10 x 1) / (10 x 10) = 10 / 100 = 0.1

(1 x 10) / (10 x 10) = 10 / 100 = 0.1

(1 x 1) / (10 x 10) = 1 / 100 = 0.01

(10 x 10) / (10 x 1) = 100 / 10 = 10

(10 x 10) / (1 x 10) = 100 / 10 = 10

(10 x 10) / (1 x 1) = 100 / 1 = 100


Belser’s example of the Nutrition Facts label, which contains facts that most people don’t understand, tells us how to apply the formula and interpret the results. “Unless you are in the medical profession, you probably don’t know how fat is metabolized or how carbohydrates exactly work,” he says and goes on to assign values for the variables. He gives a 6 (fairly high) for subject difficulty, a perfect 10 for motivation; and the lowest score of 1 to expertise and presentation. Substituting these values, we get CI = 0.6. 


He points out that if the audience has more knowledge of nutrition science and if we wish to assign a fairly high score (say 7) to expertise, then CI = 0.08. This indicates that ‘Nutrition Facts has greater communication value for a more expert audience’.


Plain Language

William Dubay defines readability as the ‘ease of reading created by a literary style that fits the reading level of the audience’ (Smart Language 6). Belser says that readability is just one aspect of presentation. Layout and design are other aspects. Martin Cutts has a few guidelines for effective presentation. Here is one: “Organize your material in a way that helps readers to grasp the important information early and to navigate through the document easily.” (Oxford Guide To Plain English 132). Here is another: “Consider different ways of setting out your information.” (143). He suggests 10 reader-centred structures and recommends the use of lists, tables and algorithms.


The quantitative measures of plain English have to be used along with the qualitative principles in gauging the simplicity of a text and the grade level of the audience. But readability formulae restrict themselves to the measure of text difficulty (the exception being Flesch’s Human Interest score). Belser’s Communication Index has a broader perspective, as we have seen; and, in his own words, “The Communication Index gives you the equivalent of a Ph.D. — the ammunition you need to defend your efforts to improve communication.”   




Belser, Burkey. ‘The Communication Index’ June 2006. Internet:


Cutts, Martin.  Oxford Guide To Plain English, New Delhi: Oxford University Press, 2008 (second ed.)

Dubay, William. Smart Language, Costa Mesa, California: Impact Information, 2007.

Flesch, Rudolph.  ‘A New Readability Yardstick’, Costa Mesa, California: Unlocking Language, Ed. William Dubay, Impact Information, 2007.

Gunning, Robert. How To Take The Fog Out Of Writing. Bombay: Taraporevala Publishing Industries,  1979 (rpt).




One Response to “Burkey Belser’s Communication Index”

  1. bdubay Says:

    This is an excellent approach that makes use of the features of text as outlined in Gray and Leary’s “What Makes a Book Readable” and the features of the reader as outlined in the many works of George Klare.

    What would help is some evidence or study showing the reliability and validity of the formula.

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