The importance of credibility in human communication had already been recognized long before modern communication research emerged as a scientific discipline. For ancient rhetoricians like Aristotle or Cicero it was self-evident that the credibility of a communicator had an important impact on the persuasiveness of his performance. At the beginning of the twentieth century credibility became a central concept in communication research, first in propaganda, later in other areas such as advertising or political communication. Today, the field of research is quite complex: different research traditions have bred a considerable number of definitions, operationalizations, and findings. Three major models of credibility can be distinguished: the source model, the recipient model, and the experience model. Modern research has come to the conclusion that there is no linear relationship between the credibility of a communication source and the effectiveness of its persuasive efforts. The magnitude as well as the persistence of credibility effects depend on several intervening variables.
Carl I. Hovland (1954, 1071)stated that “who says something is usually as important as what is said in the determination of the impact of a communication.” However, the effects of both the communicator and the message depend largely on the perception of the third core element of every communication model: the receiver. Credibility is a perceptual state, i.e., the outcome of an attribution process in which recipients of messages form judgments about their sources and therefore assess them as credible or not. The perceived credibility of a communication source depends on the perception and attribution by the receiver: a message source may be regarded as highly credible by one person and not at all credible by another.
The source model focuses predominantly on the communication source: credibility is considered as the result of the pre-existing or perceived characteristics of a source. A rudimental version of this model can be found in Aristotle’s ground-breaking treatise on rhetoric in the fourth century bc, in which he argued that trustworthiness, good will, and wisdom make a communicator appear credible and threrefore facilitate persuasion. The concept of credibility actually first appeared in the Yale Studies, a series of psychological experiments conducted by Hovland and his colleagues in the 1940s and 1950s: credibility was conceptualized as a composition of several (perceived) communicator characteristics – especially the communicator’s expertness and trustworthiness. Later researchers have tried to identify additional source characteristics, e.g., qualification, fairness, similarity, physical attractiveness, and dynamism (e.g. Berlo et al. 1969). Although the model provoked intense criticism (e.g., Cronkhite & Liska 1976), it gained much attention in communication research.
The recipient model focuses predominantly on the recipients’ traits: the perception and attribution of a source’s credibility are likely to differ between different recipients. Thus it depends on the recipients’ predispositions whether a message source is perceived to be credible or not. Hovland and Janis hypothesized the existence of an individual predisposition called general “persuasibility”. The term “refers to a person’s readiness to accept social influence from others” (Hovland & Janis 1959, 5). It was assumed that women and individuals with low levels of intelligence or self-confidence were generally more persuadable. However, no significant evidence for the existence of a general persuasibility as a personality trait could be found. Later research focused on other traits such as dogmatism which can be defined as individuals’ tendency to “close off their minds to new ideas and accept only the opinions of conventional, established authorities” (Perloff 2003, 219). Research indicated that dogmatic persons were more susceptible to persuasion than others. However, until today there has been no commonly accepted empirical procedure for identifying persuadable individuals. In addition, no sustainable evidence about the existence of general persuasibility or its correlates could be found (O’Keefe 2002, 242).
The experience model emphasizes the interaction between message source and recipient. According to Niklas Luhmann (1989), credibility serves as a heuristic that helps to reduce social complexity. Based on positive experiences with communication sources, individuals attribute credibility to them. By this, they avoid engaging in arduous investigations to find evidence for the trustworthiness of the respective source. Credibility is defined as an outcome of frequently practiced pseudo-empirical tests which are part of every individual’s life. This “inductive knowledge” (Simmel 1990) leads to experience-based expectancies toward message sources. Credibility is thus the result of learning: individuals believe in a person or institution because they have learned that they can do so without experiencing negative consequences.
Effects Of Credibility
In early research a linear relationship between source characteristics and the persuasiveness of its messages was usually assumed: the more credible a source was perceived by its users, the more effective its messages would be (e.g., Berlo et al. 1969). However, the correlation between source credibility, the persuasiveness of messages, and attitude change is not as clear as is frequently assumed. Credibility effects are neither linear nor permanent. The magnitude and persistence of credibility effects varies from one case to another, depending on a considerable number of intervening factors.
When discussing the effects of credibility it has to be noted that most experimental studies compare the effects of highand low-credibility sources. Hovland and Weiss (1951) found that messages from high-credibility sources created more attitude-change than those from low-credibility sources. Subsequent studies revealed that high-credibility sources were not always more effective – their influence depended on other factors such as the position advocated in the message. High-credibility sources enjoy an advantage when the advocated point of view is opposed to the audience’s position. Low-credibility sources, on the other hand, are more successful when the position advocated is shared by the audience. Therefore the impact of both the source’s perceived credibility level and the position advocated by the source and the receiver have to be considered when explaining credibility effects (O’Keefe 2002).
Credibility effects largely depend on the recipient’s attitude toward the issues in discussion. According to contemporary information-processing models such as the elaboration likelihood model (Petty & Cacioppo 1986), the effects of persuasive communication mainly depend on the recipient’s ego-involvement. Indifferent or uninterested recipients tend to process information superficially. They rather base their judgments on source characteristics such as the communicator’s credibility. Highly involved individuals, on the other hand, search for high-quality arguments and tend to process information systematically and carefully, mostly neglecting source characteristics and focusing on the quality of the communication content. In consequence, “under conditions of low personal relevance, the communicator’s credibility may make a great deal of difference to the outcome, whereas on highly relevant topics, the source’s credibility may have little impact” (O’Keefe 2002, 192).
Furthermore, the effects of credibility depend on the availability of information about the source. The timing of the source’s identification and the revelation of information about it decide whether credibility dimensions like expertise or trustworthiness have effects on the audience. When no information about the source is provided, recipients concentrate on message cues, which leads to a minor significance of source characteristics. Sources that are usually regarded as simply not credible at all can improve the persuasiveness of their messages by delaying source identification (O’Keefe 2002).
Finally, the effects of credibility seem to decay over time. Hovland and Weiss (1951) discovered that messages of high-credibility sources lost persuasiveness after some time, leading to a lower extent of attitude change. Correspondingly, low-credibility communication seemed to be more effective at a later date than it had been directly after transmission. Regardless of many unsuccessful attempts to replicate these findings, this so-called sleeper effect gained much attention in communication research. It is assumed that message sources become forgotten or disassociated from the message. Effects of source characteristics such as expertise and trustworthiness seem to lose ground. Accordingly, long-term effects in persuasive communication are rather a result of message content than of source characteristics. However, the persuasive effects of messages also decay, but more slowly, thereby causing the sleeper effect. Although it is doubtful whether a general sleeper effect exists, it is an important finding that credibility effects probably are short-lived.
Although many questions still remain unanswered today, and although there is much criticism focused on theory and methodology, the last six decades of credibility research have produced a considerable amount of agreement among scholars concerning the nature and effects of credibility (Perloff 2003). First, most researchers agree that credibility is a perceptual variable – the result of an attribution process, not a property of a communication source. Second, there is an agreement that source credibility is a multidimensional construct, though the quantity and quality of credibility dimensions is controversial. Third, there is no doubt that under certain circumstances communicator credibility has a strong influence on audiences; however, there is no linear relationship between the (perceived) level of credibility on the one hand and the magnitude and persistence of effects on the other hand. To understand the effects of credibility in human communication it is necessary to attend simultaneously to the different intervening factors. The attribution of credibility and its effects on audiences result from a complex social interaction that includes all parts of the communication process.
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