Word of mouth has become the Holy Grail for today’s marketers. Word-of-mouth marketing, also called word-of-mouth advertising or WOM, is 10 times more effective than traditional advertising, according to Jonah Berger, a Wharton marketing professor. “A great deal of research has demonstrated that word of mouth affects choice, diffusion [the process by which a group of people adopts a product] and sales,” writes Berger.

Today, word of mouth extends far beyond face-to-face and phone conversations to texting, chatting, social media sites and blogs. How does a business find reliable suppliers or choose the best advertising agency? What about consumers deciding on a repair company to fix a broken dryer, the right store to buy an engagement ring, whether or not to try that new sports drink, when to upgrade an iPad or what product would get crayon marks off the coffee table? For many consumers and firms, it wasn’t traditional advertising that helped them make a choice, but a Yelp review, a text exchange with a relative, a spontaneous chat with a co-worker, an acquaintance’s post on Facebook or reviews on a business’s website.

But does word-of-mouth work the same way for all products and in all media? Berger and fellow Wharton marketing professor Raghuram Iyengar say no: The medium being used — oral versus written — actually influences which products get talked about. What’s more, marketers can capitalize on this knowledge to better exploit the power of word of mouth. Their findings are presented in the paper “Communication Channels and Word of Mouth: How the Medium Shapes the Message,” published in the October 2013 issue of Journal of Consumer Research.

Berger and Iyengar have both done research on word of mouth before — in fact, it was anomalies discovered in previous results that led Berger to conduct this study. “Some of my earlier research found that online, more interesting things are more likely to be shared,” Berger notes. “That makes sense. But in another paper I worked on using offline data, it didn’t seem that more interesting things were more likely to be shared. Why were we seeing one thing in one channel and one thing in another? Was it because of the different populations of those two studies, or could it be saying something about the psychology of word of mouth?”

“Some of the brands I work with say things like, ‘We could never do word of mouth because there’s nothing exciting about us.’ But people talk about the weather all the time. They talk about what they had for lunch.” –Jonah Berger

What do consumers consider “interesting,” exactly? According to the paper, products or brands are categorized as interesting when they are novel, exciting, surprising or violate expectations. Consumers actually exhibit a great deal of agreement when it comes to categorizing brands that are more interesting or more mundane. “Most consumers see iPhones as more interesting to talk about than [a brand of] ketchup, or Nike as more interesting than Tide,” Berger says. In Berger and Iyengar’s current study, products that were rated “highly interesting to talk about” included iPhones, augmented reality glasses – such as Google Glass — and laptops. Among the products rated “not very interesting to talk about” were nail polish, chairs and toothpaste.

‘Interesting’ vs. ‘Boring’

As Berger points out, common sense would suggest that “interesting” products would always get discussed more than mundane ones. But why didn’t this happen across the board in Berger’s earlier research on offline word of mouth? Could sharing online versus offline affect whether people mention more or less interesting products and brands? Berger and Iyengar put their theory to the test in three laboratory experiments and two field settings. They pitted oral communication (face-to-face or phone) against written communication (texting, messaging, tweeting and most online conversations).

In the first study, Berger and Iyengar paired up 178 college students and asked them to have a short conversation about products or brands of their choosing. Some pairs were required to talk face to face, while others used instant messaging. The researchers found preliminary support for their theory. “Merely using written rather than oral communication led people to mention more interesting products and brands,” they write.

Next, the face-to-face communicators were asked to pause for a given number of seconds before speaking. Pausing before speaking actually caused this group to mention more interesting products and brands — duplicating the effect the researchers observed occurring naturally in written communication. “In oral communication someone says something, and the other person responds relatively quickly, but written communication allows more time to construct and refine what to say,” the researchers note. “This in turn leads people to polish their communication and find more interesting things to talk about.”

In the second study, Berger and Iyengar once again tested both oral and written communication among college students. This time, however, some were asked to start communicating right away and others were asked to pause before conversing. As in the first experiment, the oral communicators who were required to pause before speaking talked about more interesting products. However, the required pause had little effect on the written communicators. According to Berger and Iyengar, this was because the written medium itself already offered them more time to construct and refine their message.

Berger and Iyengar next investigated the role of self-presentation, or self-enhancement, in the experiments. Berger explains this principle as people’s natural inclination to try to get others to think positively about them. He also calls it “Social Currency,” a term he coined in his recent book, Contagious: Why Things Catch On. “We’re more likely to share things that make us look better because it reflects positively on us,” says Berger.

“To make word-of-mouth marketing work for your company or organization, you have to understand why people talk.” –Jonah Berger

The researchers conducted the third study similar to the first two, but this time they told participants they would be evaluated at the end of the conversation. They predicted that “self-enhancement should lead people to talk about more interesting products and brands, but the effects should be stronger in written communication,” which naturally allows more opportunity to polish what is said.

Their prediction was borne out. The written communicators talked about interesting brands and products even more noticeably because they knew they would be evaluated. But the participants using oral communication did not have enough time to prepare their remarks in order to self-enhance to any significant degree. They responded “the way you would respond if someone walked up to you and asked your opinion on a topic,” write Berger and Iyengar.

Evidence from 20,000 Conversations

Following the three laboratory experiments, the authors engaged in two phases of field research. Berger and Iyengar turned to the Keller Fay Group, a New Brunswick, N.J.-based market research firm that helps clients capitalize on word-of-mouth and social influence. They analyzed data on how frequently 5,960 consumers mentioned 1,212 products and brands — everything from giants like Coca-Cola and Walmart to smaller brands like Jack Link’s beef jerky and Nestlé Toll House cookies — broken down by oral and written communication. Then they extended their research to a richer, individual-level data set that included 8,000 products and brands, and nearly 20,000 conversations.

The result reported by Berger and Iyengar was that real-world word of mouth, generated by thousands of people across thousands of brands, was consistent with what they had uncovered in the laboratory. “The relationship between interest and word of mouth differed by communication modality,” they write. Berger adds: “The more interesting something is matters for online sharing, but it doesn’t seem to matter much, if at all, for offline sharing.”

The Keller Fay data also yielded some additional information about what oral communicators tend to talk about. People having a conversation — which affords little time to plan what to say and how to respond — are more likely to mention products or brands that are top-of-mind or are “triggered” by the surrounding environment. Just like saying, “Peanut butter and …” will remind people of jelly, seeing something in the surrounding environment may lead people to talk about related topics or ideas.

Berger gives an example of a recent campaign for a candy bar that he says successfully capitalized on triggers by linking their product to coffee. “Think about a coffee break; think about Kit Kat. Kit Kat and coffee, coffee and Kit Kat. Did that make Kit Kat seem really exciting? No. Is it going to make people talk about it a lot online because it’s interesting?” Berger asks. “Not really. But that campaign got huge word of mouth offline because it triggered people to think about Kit Kat every time they were having coffee.”

When conducting word of mouth advertising, marketers can refine their approach by drawing on the paper’s findings, according to the researchers. Marketers could determine if their product is “interesting” or “less interesting,” and direct their dollars accordingly.

If the product is interesting, the goal could be getting more online discussion through ads or online content that surprises people or violates expectations. “You’re writing a kind of press release or story that you hope people share online to talk about how remarkable [a product] is. Make it Social Currency to share it — make it seem exciting and new,” says Berger.

“The more interesting something is matters for online sharing, but doesn’t seem to matter much, if at all, for offline sharing.” –Jonah Berger

But if the product falls into the category of “less interesting” or mundane, then making the product more accessible in consumers’ minds, or publicly visible, may be a better way to spend a marketing budget. The goal would be to trigger people to think about the product during on-the-spot, face-to-face discussions — such as workplace interactions, similar to the Kit Kat campaign.

“Some of the brands I work with say things like, ‘We could never do word of mouth because there’s nothing exciting about us,’” Berger notes. “But people talk about the weather all the time. They talk about what they had for lunch. It’s not that these are the most exciting things in the world; it’s that they’re top of mind, and people are thinking about them. So that’s a great way to get people to share as well, particularly offline.”

According to Berger, the paper’s findings can also be applied to business negotiations and other interpersonal communications. “If we’re negotiating and we need time to refine what we’re going to say, online may be better than offline. That said, if we’re trying to get people to speak off the cuff, be frank and honest, offline may be a better way to go because it will get people to talk about what is top of mind rather than just what makes them look good.

“To make word-of-mouth marketing work for your company or organization, you have to understand why people talk in the first place,” Berger adds. “Word of mouth is an extremely effective tool, but to make it work for you, you have to understand what drives people to share.”