When it comes to influencing others delivering the right number of messages to support your proposal or proposition is going to be crucial. Too few and your attempt might come across as halfhearted, indifferent or plain weak. But too many messages can hurt you too. Like adding too much spice to the dish, your influence attempt could become overpowering—one that even the dog will turn his nose up at.

So when it comes to successfully persuading others, what is the optimal number of claims that you should employ to produce the most positive impression? The match offers worked. Karlan and List found that offering a match increased the probability that each recipient would give by 19%, and that the average gift increased by 22%. Pretty impressive gains, but then the surprises start.

One potential answer to this question comes from a brand new study conducted by researchers Suzanne Shu from UCLA’s Anderson School of Business and Kurt Carlson from the marketing department at Georgetown University. In their studies participants were assigned to one of six groups and asked to read descriptions of different five target objects – a breakfast cereal, a restaurant, a shampoo, an ice cream store, and a politician. (Let’s save the ‘Is a politician an object?’ debate for another day).

As an example the shampoo advertisement was introduced as follows:

“Imagine that you are reading one of your favorite magazines and an ad for a new brand of shampoo catches your attention. You decide to read the ad carefully to see if it is worth switching to this new product. The ad says that this new shampoo does the following:

The space below the text was then filled with one, two, three, four, five or six positive claims about the shampoo object. For example participants who were shown all six claims read “Makes hair cleaner, stronger, healthier, softer, shinier, and fuller”.

Similarly, in the political advertisement, participants who were shown all six claims read that he was “honest, had integrity, experience, intelligence, interpersonal skills, and a desire to serve.”

After seeing the ads the attitudes of each participant toward the target objects were measured along with how positive or negative their impressions for each were. The researchers also measured levels of scepticism in an attempt to identify the point at which people started to think that the claims on the ads where just a ploy to persuade them.

The results clearly demonstrated that those who had read three claims rated all the items (regardless of whether they were shampoos or politicians) significantly more positively than participants who had read adverts with one, two, four, five, or six claims. So it would appear that adding additional positive claims to a persuasive appeal increases the effectiveness of that appeal but only until the third claim is reached. But beyond three, further persuasion attempts increase scepticism which, in turn, can heighten resistance to the overall persuasion appeal.

This squares with another recent study, this time conducted by Daniel Feiler, Leigh Tost and Adam Grant, for the Make-A-Wish Foundation. Participants were randomly assigned to receive a request to donate to the charity that had either two egoistic reasons to give, two altruistic reasons or all four reasons combined. Giving intentions were much lower in the group who were provided with four reasons to donate with post study surveys revealing a simple reason why. People could see the persuasion attempt for what it was—an attempt to influence them. More evidence that when crafting a persuasive communication there comes a point when adding additional arguments and justifications acts to heighten resistance which, in turn, can greatly reduce its impact.

So the answer to the question “What is the optimal number of claims that should be used to produce the most positive impression?” seems to be three.

Or, as Shu and Carlson so succinctly write, “three charms but four alarms.”

Sources:

At the time of writing the Three Charms, Four Alarms paper was awaiting publication. We were provided with the following suggested citation: Carlson, Kurt A. and Shu, Suzanne B., When Three Charms But Four Alarms: Identifying the Optimal Number of Claims in Persuasion Settings. http://dx.doi.org/10.2139/ssrn.2277117

More details of the experiments combining egotistic and altruistic appeals can be found in: Feiler, D. C., Tost, L. P., & Grant, A. M. (2012). Mixed reasons, missed givings: The costs of blending egoistic and altruistic reasons in donation requests. Journal of Experimental Social Psychology, 48(6), 1322-1328.