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.

Sunday, February 22, 2015

Credibility is Convincing



This is an advertisement which persuades the viewer to purchase Dove’s Advanced Care deodorant by using a credible source to explain the product’s benefits. A dermatologist, Dr. Ellen Marmur, explains that the product is good for the skin because it contains humectants, which help to moisturise the skin.

Hovland and Weiss (1951) provided empirical evidence to show that using a ‘high credibility’ source to convey a message is more convincing than using a ‘low credibility’ source. Participants were given questionnaires asking them for their opinions on four controversial topics, The Future of Movie Theatres, Atomic Submarines, The Steel Shortage and Anti-Histamine Drugs. The questionnaire also asked them to rate how trustworthy they found various sources.

Participants were then shown one article for each of the four topics. The version of each article that participants were shown either had an ‘affirmative’ or ‘negative’ stance on the subject, and was either attributed to a source which the experimenters viewed as being high or low in credibility. For example, the high credibility source for the Anti-Histamines topic was a scientific journal of biology and medicine, whereas the low credibility source was a pictorial magazine. Each source had been included in the previous questionnaire which asked participants to rate the trustworthiness of various sources. After reading the articles, participants answered another questionnaire which again asked for their opinions regarding the topics.

Table 1














Table 1 shows the results. A greater net percentage of participants changed their opinion to agree with the article when a high credibility source was used than when a low credibility source was used. For example, with the Anti-Histamines article, 22.6% of participants changed their opinion to agree with the article when the source was high credibility, but 13.3% did this when the source was low credibility. The difference between the average percentage changes was 16.4%, and this was significant at p<.01.


Table 2












Results were also analysed in a different way. The independent variable was whether participants had previously rated the source of the article as trustworthy or not, and the dependent variable was the net percentage of participants who changed their opinion to agree with the article. Table 2 shows the results, which were consistent with the results from the previous analysis, as participants showed a greater net change of opinion towards that of the article when the source had been rated as trustworthy than when it had not. For example, with the Anti-Histamines article, 25.5% of participants changed their opinion to agree with the article when they had previously rated the source as trustworthy, but 11.1% did this when they had not. The difference between the average percentage changes was 14.1%, and this was significant at p<.03.

Therefore, the advertisement for Dove’s Advanced Care deodorant is effective because it uses a credible, trustworthy source.

Reference

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

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