Behaviour Change

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

Thursday, January 23, 2014

Chair-worthy hair

We've all seen countless numbers of haircare ads, each one almost certainly featuring a lady with abnormally shiny hair. This one by TRESemm√© is no different, but something thing that does stand out is the way it’s narrated by someone in the role of a hairstylist, that is, someone who has professional expertise in this area and whose opinion we think is credible. Communicating the wonders of the product from an expert’s point of view gives us the impression that the argument is valid. This works by putting us in the role of someone who is ‘not in the know,’ so that we don’t feel we have enough knowledge to evaluate the information presented to us, and end up relying on the expert’s opinion.

To illustrate, a well-known study by Hovland and Weiss (1951) found that presenting participants with information on a topic from a highly credible source (a scientific journal) lead to a significantly greater change in opinion, compared to those given identical information from a less credible source (a tabloid). In this case, if at first we are sceptical of the advert’s bold claims, its use of a credible source should make us more prone to being convinced the products really do repair split ends. If it’s good enough for a professional, then it’s good enough for us.

Of course, the creators of the advert have backed this up with the opinions of regular customers. Here, they include the statistic ‘100% of 30 women agreed,’ taking advantage of social proof, one of Cialdini’s (2007) six principles of influence. This phenomenon arises due to our need to look to the behaviour of others in a given situation in order to inform our own actions. Numerous studies have shown how knowledge of others supporting a cause or action can have significant impact on social agreement (Pratkanis, 2007). Since the whole sample of women used in the TRESemm√© advert thought the products were effective, we are less inclined to evaluate the product for ourselves and instead rely on the opinions of these women and agree.

Furthermore, Wang (2005) demonstrated that it’s the positive ratings by regular customers rather than experts that enhances behavioural intent when the consumer is already interested in the product. So unfortunately, if you happen to be in need of a new shampoo and this TRESemm√© offering has caught your eye, hearing others have enjoyed the product not only makes us think more highly of it, but also increases the likelihood of us actually going out and buying it ourselves.


Cialdini, R. B. (2007). Influence: The Psychology of Persuasion. New York: HarperCollins.

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

Pratkanis, A. R. (Ed.). (2007). Social influence analysis: An index of tactics. The science of social influence: Advances and future progress. New York: Psychology Press.

Wang, A. (2005). The effects of expert and consumer endorsements on audience response. Journal of Advertising Research, 45(4), 402-412.

Charlotte Chan

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