Viral Credibility

Recent outbreaks of measles in the U.S. have sparked a growing national debate about childhood vaccinations.
Viral Credibility
Recent outbreaks of the measles in the U.S.—the largest traced back to the Disneyland amusement park in California—have sparked a growing national debate about childhood vaccinations. The central question: Why are more parents choosing not to vaccinate their children, especially against the recommendations of their doctors?

One reason might be “electronic word-of-mouth” or eWOM, say assistant marketing professor Ioannis Kareklas, marketing professor Darrel Muehling, and doctoral student T.J. Weber, all of Washington State University’s Carson College of Business in Pullman. While word-of-mouth has long been one of the most effective forms of advertising, eWOM is a “relatively new phenomenon” that can exert great influence over consumers, even among strangers. In fact, many parents might give as much credence to online comments as to websites and public service announcements (PSAs) from official medical sources.

The three researchers showed 129 study participants two fictional PSAs, one pro-vaccination and one anti-vaccination. Participants were told that the pro-vaccination PSA was sponsored by the U.S. Centers for Disease Control and Prevention; the anti-vaccination PSA, by the National Vaccine Information Council. Each PSA was designed to look as if it had appeared on its respective organization’s website.

The PSAs were followed by comments from fictitious individuals who expressed either pro- or anti-vaccination views. Participants had no information about commenters; to avoid gender biases, each commenter had a name suitable for either a man or woman.

After reading the PSAs and comments, participants filled out questionnaires where they indicated their opinions about vaccination. The researchers found that statements made by online commenters wielded a great deal of nfluence. “People trusted the random online commenters just as much as the PSA itself,” says Kareklas.

In a second experiment, participants were told that a healthcare industry lobbyist and an infectious disease specialist were among the commenters. In this instance, participants were persuaded by the comments more than by the PSA.

To account for the influence of online comments, marketers need to take three important steps, the researchers advise. First, they should include opposing points of view when relevant, so that readers do not perceive their messages as manipulative. Second, they should highlight supporting comments from experts in relevant fields. And, finally, they should use online strategies that encourage credible dialogue, collaboration, and problem solving, while discouraging contention and controversy.

“Re-examining Health Messages in the Digital Age: A Fresh Look at Source Credibility Effects” was published online in May by the Journal of Advertising. It is available for download at