Advertising/Promo/Spot Frequency


I received this question for my "Research Doctor" column on and decided to print it here since I am asked this question so often.


Doctor:  Somewhere I read about a formula used to calculate the number of impressions needed for a spot or promo to really sink in.  You were supposed to multiply cume by 3.4 and do something else and it would give you a right-on number of promos to run.


Do you know anything about this or where I found it?  Thank you! - Anonymous


Anon:  I’m sure you didn’t anticipate that your question would open a giant can of night crawlers, but it did.  I suggest that you get a glass of your favorite beverage because this answer is not a brief one.


However, before I get to your formula, I need to step back a bit and discuss the fundamental base of your question—persuasion.  We need this because we need to know what persuasion is and how it works.  I have a detailed article on persuasion on my business website, but I’ll summarize a few things here for simplicity.


First: Persuasion is communication, and communication is persuasion (that comes from Aristotle, the dead ancient dude).  We cannot not communicate (that comes from Watzlawick, Bavelas-Beavin, and Jackson, 1967), and therefore we cannot not persuade (that comes from logic using the first two statements).  That’s what you are trying to do with your spots or promos—persuade listeners to do something, buy something, believe something, or whatever.


Second: How do people make decisions or eventually believe in or perceive something?  The information here comes from persuasion research, and what we know is that people pass through five stages of communication/persuasion in order to make a decision.  The stages are: Unawareness, Awareness, Comprehension, Conviction, and Action.


The “Action” stage is where people buy a product, try a new radio station, believe in something, or whatever.  It is the culmination of information received from one or many sources.


OK.  Do you have that so far?  All people…all people...pass through five stages in the communication/persuasion process for any decision.  This is universal and it is a rule without exception.


We understand the communication/persuasion process very well.  Specifically, we know that all people pass through the stages before making a decision, and we know that in order to get people to pass through the stages, there must be repetition of the message.  One exposure may work for some things—“I’ll give you $1 million if you recite the alphabet backwards.”—but in virtually all other cases, multiple exposures are required.


How many exposures?  Well….therein lies the problem.  We don’t know.  While we do know a lot about how the communication/persuasion process works, we don’t know (and can’t predict) how many message exposures are necessary to move people through the stages.  That’s the fact, Jack, and there is no one in the universe who knows or can predict the correct number.  No one.  Nada.  Zilch.


Now…some people never get to the Action stage even after hundreds or thousands of exposures.  I can verify this with my youngest son, Buckwheat, who, after hearing thousands of times that “The grass needs to be cut on Saturday” never got the message.  He had to be reminded every Saturday, and I’m sure he is happy to be living on his own now.


OK, back to your question about 3.4 exposures to a message.  If we know how persuasion works, but we don’t know how many exposures are necessary to reach the Action stage, then where in the heck did this stuff come from about 3.0 or 3.4 exposures?  Who started this falsehood?


To find that answer, we need to flashback to the 1960s and 1970s.  Two people are credited for the information about the number of exposures necessary.  The only problem is that they are falsely credited.


1.  In 1966, Colin McDonald, then working for the British Market Research Bureau in London, conducted a research project for J. Walter Thompson about advertising.  McDonald’s study was about the relationship between advertising exposures and buying behavior, NOT the frequency of advertising messages required for a campaign.  But that is how the study was interpreted.


2.  In 1972, Dr. Herbert Krugman, then head of market research at General Electric, published an article in the Journal of Advertising Research about how consumers pass through three stages in their response to advertising.  This information was falsely equated to the McDonald research about three exposures, and the urban legend about three exposures took off.


In later writings, both McDonald and Krugman explained that their research was misinterpreted.  But that didn’t matter.  Three exposures became the “rule of thumb.”  In reality, however, three exposures became the law for anyone involved in media advertising.  A “law” based on misinformation or misinterpretation of data.  Neat, eh?


3.  In 1995, Professor John Philip Jones (Syracuse University, S.I. Newhouse School) published a book, When Ads Work that encouraged a rethinking of the three exposure “rule of thumb.”


One characteristics of scientific research is that it is self-correcting.  Any research finding is always open for further research, and the further research may debunk previous findings.  In the case of the three exposure “rule,” the results have been debunked (and corrected), but the belief that three exposures is “right” still continues.


So here is my final answer, Regis, to your question about the frequency formula:

  1. Forget the formula. It’s wrong and so are all the other formulas that suggest the correct number of exposures.  All of the formulas are based on urban legend, folklore, misinformation, and Vulpes Fulva leavings.  Forget ALL of them.

  2. Air as many promos as you can because you don’t know how many you need.

  3. Your decision will be as “right” as the person who says you need 3 exposures, or 10 exposures, or any other number.

OK.  The basics are done. But I want to add a few things:


In the course of searching for information to answer your question, I found some very interesting things that you might wish to pursue:


1.  In a 1997 article by Paul Feldwick entitled, How many ads are enough?, in which he discusses the three exposure “rule,” he states:


“It may seem surprising that a mistaken interpretation of data can lead to a generally held belief which remains uncorrected, even by its original author, for some thirty years. But anyone who reads this book [McDonald’s rewrite] with attention will understand how easily and frequently ‘effective frequency’ debates can be misunderstood and misrepresented by those who attempt to reduce the complexity of the evidence to simple rules.


2.  There is an interesting study funded by Microsoft that investigates the optimal number of exposures required for audio messages.  The study found that somewhere between 6 and 20 exposures are best.  (But that doesn’t mean the study is correct.  Remember, a characteristic of scientific research is that it is self-correcting.)


3.  Search the Internet for (use the quotes) “Colin McDonald” three exposures and  “Dr. Herbert Krugman” three exposures for more information about the three exposure rule of thumb.

Wimmer Research (