The Effects of Source Credibility in the Presence or Absence of Prior Attitudes: Implications for the Design of Persuasive Communication Campaigns.

Designing effective communications supposes an understanding of how the intended audience might react to a specific content or type of communicator (e.g., Albarracin et al., 2005; Centers for Disease Control and Prevention, 2001; Durantini, Albarracin, Mitchell, Earl, & Gillette, 2006; National Cancer Institute, 2001; Petty & Cacioppo, 1986). One critical aspect of this understanding is whether and for whom the credibility of a communicator matters. For example, groups with established attitudes about an issue may differ from groups without such attitudes, requiring more or less attention to the communicator selection. The present paper addresses this important yet understudied issue. Classic theories of attitudes (e.g., social judgment theory, Sherif, Sherif, & Nebergall, 1965; information integration theory, Anderson, 1981), assume that initial attitudes can exert powerful influences when individuals evaluate new information. Despite this widespread assumption, there is partial knowledge on the impact of having versus not having initial attitudes about an object on the processing of later information about that object (for similar observations, see Albarracin, Wallace, & Glasman, 2004; Chaiken, Liberman, & Eagly, 1989; Chaiken, Wood, & Eagly, 1996). Specifically, most of the past research on this topic has concentrated on identifying how prior attitudes bias the evaluation of persuasive communications (Chen & Chaiken, 1999; Petty & Cacioppo, 1986; Pratkanis & Greenwald, 1989). However, past research has not clearly established whether people who possess prior attitudes utilize the same types of information as people who lack prior attitudes. In the present study, we are interested in how the credibility of a source influences attitudes about the topic advocated by that source, and the degree to which these influences may be attenuated by the presence or absence of prior attitudes. Specifically, assessing the credibility of external sources is particularly important in the absence of prior information about the issue. Hence, the credibility of the communicator should be most influential when one is unable to access a prior attitude about the topic and does not construct a personal attitude online based on, for example, the message content (e.g., Chaiken & Maheswaran, 1994; Mackie & Worth, 1989). In contrast, if people have established attitudes about the object, those attitudes are likely to provide readily available, subjectively valid bases for a current evaluation of the object (Albarracin et al., 2004; Eagly & Chaiken, 1993; Fazio, 2000; Kruglanski, Webster, & Klein, 1993; Pratkanis & Greenwald, 1989; Sanbonmatsu & Fazio, 1990). Similarly, repeated exposure to the message or having extensive knowledge about an issue should allow people to form a new attitude on those bases (Wood, Rhodes, & Biek, 1995). Therefore, prior attitudes, prior knowledge, or repeated exposure to the message may reduce the influence of source credibility. One reason is that prior attitudes, knowledge, and message content are generally perceived as being more valid bases for judgment than is the credibility of the source. In the present study, we test this prediction by meta-analytically integrating the effects of source credibility as a function of whether or not message recipients (a) have initial attitudes about the issues discussed in the communications; and (b) are likely to form online attitudes based on the message content. The likelihood of forming attitudes online is inferred from the presence or absence of message repetition, the availability of prior knowledge on the message topic, and outcome relevance. Importantly, because the effects of source credibility are likely to fluctuate over time, it is imperative to test our predictions not only immediately after the communication, but also later in time. Observing the stability of the effects of source credibility allows us to make some inferences about whether the effects are elaborative (i.e., greater maintenance) or nonelaborative (i.e., greater decay; Petty & Cacioppo, 1986). Therefore, as described presently, the scope of this meta-analysis is restricted to studies that included measurement of attitudes at least twice after message exposure.