Source Credibility

The Sleeper Effect

One of the early important findings on source credibility was Hovland's “sleeper effect,” which showed that a message from a low-credibility source may become more believable across time as the link between the message and the source fades. This somewhat counterintuitive finding has many practical applications in modern political campaigns, in which unknown (noncredible) political action committees run deceptive ads. According to the sleeper effect, such ads will be persuasive in the long term because their message will remain after its original source is forgotten. Later research suggests that this effect only occurs when the message is persuasive and has an impact over time, the discounting cue is large, and enough time has passed. One way to reduce this deception would be to remind the audience of the low credibility of the original source.

Typically, the impact of source credibility is measured by presenting research subjects with a message given by message communicators of variable credibility. The impact of credibility is measured by changes in subjects' beliefs, behavioral intention, or decision making. A meta-analysis indicated that while source credibility only has a relatively small effect on persuasion (4.5 percent of the variance), the combination of source, message, involvement, and the listener has a larger collective effect.

Source credibility's power is centralized in the communicator-listener interaction. While individual characteristics of the communicator, such as perceived expertise and trustworthiness, have been found to increase source credibility, such characteristics do not exist in a vacuum. [Page 856]Perceived expertise depends on the message being communicated: the more consonant the message is with characteristics of the communicator, the more expertise will be perceived. For example, a message about the reliability of memory, from a person with published research in the area of memory, would likely be seen as credible.

In turn, the importance of the message is often a function of the listener's involvement in the message: the more identifiable a message is with a trait or concern of the listener, the more the message will be perceived as important. For example, a person with a specific health issue is more likely to listen to messages about that issue than a healthy person would.

Credibility and Persuasion

Modern inquiry of source credibility also owes a large debt to Richard Petty and John Cacciopo's experiments in the late 20th century on credibility and persuasion. Their work demonstrated that source credibility is most important when listeners either are relatively uninvolved in the message content or unable to process the complexity of it. Conversely, source credibility is least important when listeners are heavily involved in a message, especially one that they perceive they understand well. Additionally, listeners who are presented with a message they disagree with might reject it more vigorously when it comes from a credible source than from a less credible source.

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