Source: William Brady & Jay Van Bavel—New York University

Decades of social psychological research sought to understand a fundamental question that pervades our social life including politics, marketing and public health; namely, how are people persuaded to change their attitudes towards an idea, person, or object? Traditional work found that there are key factors that influence whether persuasion is successful or not including the source of the persuasive message ("source"), and the argument content of the message ("content"). For example, expert sources and messages with sound arguments are typically more persuasive. However, as more studies were conducted, conflicting findings began to arise in the field: some studies found that expert sources and good arguments were not always required for successful persuasion.In the 1980's, psychologists Richard Petty, John Cacioppo and their colleagues proposed a model to account for the mixed findings in studies on persuasion.^1,2 They proposed the Elaboration Likelihood Model of persuasion, which stated that persuasion occurs via two routes: a central route or a peripheral route. When persuasive messages are processed via the central route, people engage in careful thinking about the messages, and therefore, the content (i.e., the quality of the argument) matters for successful persuasion. However, when messages are processed via the peripheral route, the source (e.g., an expert source) is more important for successful persuasion.

If people are motivated to pay attention to the message topic, they tend to process the message via the central route, and thus message content is more important. On the other hand, when people are not motivated to pay attention to a message topic, the message is more likely to be processed via the peripheral route and thus the source of the message is more important. Inspired by Petty, Cacioppo, and Goldman, this video demonstrates how to design a task to test different routes to successful persuasion using messages.¹

1. Participant Recruitment

1. Conduct a power analysis and recruit a sufficient number of participants (e.g., the original study used 145) and obtain informed consent from the participants.

2. Data Collection

1. Give participants the cover story for the study.
   1. Explain that the study is about assessing the quality of taped recordings discussing whether the university should institute an academic policy change.
   2. Further explain that the psy

The results showed a main effect of argument quality: The strong arguments lead to greater agreement with the message than weak arguments. There was also a main effect of source: Averaged across the other conditions there was greater agreement for the message when the source had high expertise than when the source had low expertise. However, of particular interest was the discovery of an interaction effect (Figure 1). When participants were in the high-releva

In the debate over what factors lead to a message being persuasive, this experiment provides a careful test of the idea that motivational factors, such as personal relevance of the message, play a pivotal role in determining the impact of factors that generally affect persuasion, including source characteristics and argument quality. The result of this experiment and the Elaboration Likelihood Model that took hold because of its results, steered the field in a new direction when it was in a battle over whether source cha

1. Petty, R. E., & Cacioppo, J. T. (1984). Source Factors and the Elaboration Likelihood Model of Persuasion. Advances in Consumer Research, 11, 668-672.
2. Petty, R. E., Cacioppo, J. T., & Goldman, R. (1981). Personal involvement as a determinant of argument-based persuasion. Journal of Personality and Social Psychology, 41, 847-855.