Behaviour Change

PROPAGANDA FOR CHANGE is a project created by the students of Behaviour Change (ps359) and Professor Thomas Hills at the Psychology Department of the University of Warwick. This work was supported by funding from Warwick's Institute for Advanced Teaching and Learning.

Tuesday, February 24, 2015

A Sensodyne a day keeps the dentist away

In this advert a man identified as a dentist, dressed as a dentist and sitting in what appears to be a dental surgery gives advice about what is best for your dental care. As someone who's experience with teeth is pretty much limited to having them, it seems fairly obvious that someone who spent 5 years studying them is going to know more about it than I do. His position as a dentist, and the knowledge about teeth that causes me to assume he has, makes him a credible source when it comes to oral hygiene.

Credibility of the source has long been known to be an important factor in persuading people to act in a certain way. The classic experiment was carried out by Hovland and Weiss (1951). The study showed participants articles about topics they were unlikely to hold a lot of information about (for example atomic submarines and anti-histamines. Participants were told these articles either came from high credibility sources (e.g. The New ~England Journal of Biological & Medicine) or low credibility sources (e.g. Pravda, a Soviet news magazine). As the figure below (taken from the original Hovland & Weiss, 1951, article) shows, high credibility sources were shown to cause much more change in attitude than low credibility sources were. This would suggest that Sensodyne were right to have a dentist advertise their product, as people are more open to having their opinions changed by a high credibility source. This has been explained through the mechanism of informative social influence, which explains people's conformity through the desire to hold the right opinion. We believe credible sources are more likely to be right than we are, so we change our opinions to be in line with theirs.



However, the advert may not be as persuasive as Sensodyne had hoped because, as can be seen in the diagram, the effectiveness of the high credibility source in maintaining people's attitude change over time is not as good as that of a low credibility source. For the sake of Sensodyne, I hope most people buy their toothpaste at more than month intervals!


Hovland, C. I., & Weiss, W. (1951). The influence of source credibility on communication effectiveness. Public Opinion Quarterly, 15, 635-650.

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