Smoking adverts ranging from 1920’s to 1950’s use source credibility of doctors, dentists and psychologists. Research by Hovland and Weiss (1953) found that participants were more persuaded on issues including the sale of antihistamine drugs and atomic submarines when told by a trustworthy and credible source. This links with informational social influence, the need to be right. Associating health professionals with particular tobacco brands persuades individuals that through buying this product they are making the "correct choice". In a field study by Bickman (1974) passers by on a street were more likely to complete a small inconvenient task when asked by an experimenter in a guard uniform, compared to an experimenter dressed in shirt and tie. This study demonstrates that the appearance of authority is enough to lead to increased compliance. Therefore the image of a professional on these adverts could be persuasive itself.
Bickman, L. (1974). The social power of a uniform. Journal of Applied Social Psychology, 4, 47-61.
Hovland, C. L., & Weiss, W. The Influence of source credibility on communication Effectiveness. The Public Opinion Quarterly. 15 (4) 635-650.