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Source Credibility


Source credibility has been defined within the persuasion literature as "judgments made by a perceiver concerning the believability of a communicator" (O'Keefe, 1990, p. 130-131).

In health communication, source credibility or believability can increase the effect of the message delivered, including ultimately on behavior but also on antecedents such as beliefs and attitudes (Pornpitakpan, 2004). In the dual processing Elaboration Likelihood Model, perceived source or communicator credibility may serve as a peripheral cue or heuristic by which receivers make quick judgments about a message (Petty & Cacioppo, 1986). They may do this without centrally processing the strength of the arguments in the message. Of course, other variables being equal, messages perceived to include both credible sources and strong arguments are most likely to affect audiences. Furthermore, although message argument strength and source credibility are separate variables, each may interact with and affect perception of the other (Slater & Rouner, 1996).

Identifying what is included as a "source" and what is included as a dimension of credibility are central to understanding this variable and its measurement. Delimiting what is a source depends on whether the question is being answered from a psychological or ontological perspective (Sundar & Nass, 2001).

Ontologically, a source is defined by its function or what it does. For example, scholars have distinguished between an "internal" source or the communicator originating the message and an "external" source or the medium transmitting the message. Internal sources have included, individuals, groups, organizations or institutions, and even labels (e.g., "liberal") (Sundar & Nass, 2001). Psychologically, the source of a communication is "what the receiver imagines the source to be" (Sundar & Nass, 2001, p. 54). The introductory definition of source credibility used in this entry supports an individual, psychological perspective of source as whom or what is perceived as the communicator.

Recognition of individuals, groups, and organizations as ultimate communicators or sources is more intuitively obvious than media as communicators or sources. The role of media as source is made less ambiguous when the distinction is made between credibility of types of media (e.g., television as compared to the Web) and the credibility of a single media organization (e.g., a hometown newspaper). If simply "television" is identified as the source, credibility will be based on the credibility an individual assigns to television as a medium. The sarcasm, "If it's on TV then it must be true," illustrates assignment of credibility to a whole medium. But even when a separate "internal" communicator is identified as source, the medium through which the message is transmitted can affect perceptions of that source's credibility (Pornpitakpan, 2004). That perceptions of credibility may vary when a single media organization is imagined to be the source is readily illustrated for most people in comparing, say, news from the Wall Street Journal to news from the National Enquirer.

Three source credibility scales are included, below. Berlo's (1969) and McCroskey's (1966) scales were developed based on individual speakers as sources and within a framework of persuasion. Meyer's (1988) scale was developed based on individual newspapers as sources, and so necessitates a theoretical framework that includes functions other than persuasion, such as to inform. In addition to these scales, dimensions used in studies that include organizational credibility and Web site credibility are listed.

The dimensions included in each scale vary, even between the two scales developed based on individual speakers. Early research on source credibility by Hovland (1953) postulated a two dimension construct of trustworthiness and expertise, and several studies have supported this conceptualization. However, other studies and scales have expanded upon and added to these dimensions, including the scales, below. As discussed under Additional Commentary, methodologies used in development of credibility scales may have contributed to variation in dimensions included across scales.

Example Measures with Reliability and Validity:

Source Credibility Scale (Berlo, Lemert, & Mertz, 1969)

  • Safety

    • Kind……………………..Cruel
    • Safe……………………...Dangerous
    • Friendly………………….Unfriendly
    • Just……………………….Unjust
    • Honest…………………….Dishonest
  • Qualification

    • Trained……………………Untrained
    • Experienced……………….Inexperienced
    • Qualified…………………..Unqualified
    • Skilled……………………...Unskilled
    • Informed……………………Uninformed
  • Dynamism

    • Aggressive…………………..Meek
    • Emphatic…………………….Hesitant
    • Bold………………………….Timid
    • Active…………………………Passive
    • Energetic………………………Tired

Kaminski and Miller (1984) found alphas of .72, .72, and .85, respectively, for the scales dimensions of Safety, Qualification, and Dynamism. Applying a 5-point Likert scale to the items, Posner and Kouzes (1988) reported an alpha of .90 for the overall index. In testing construct validity, Carbone (1975) found that ratings of high- and low-credibility sources were significantly different and in the expected direction across all three dimensions.

Source Credibility Scale (McCroskey, 1966)

  • Authoritativeness

    • Reliable 1 2 3 4 5 6 7 Unreliable
    • Uninformed 1 2 3 4 5 6 7 Informed
    • Unqualified 1 2 3 4 5 6 7 Qualified
    • Intelligent 1 2 3 4 5 6 7 Unintelligent
    • Valuable 1 2 3 4 5 6 7 Worthless
    • Inexpert 1 2 3 4 5 6 7 Expert
  • Character

    • Honest 1 2 3 4 5 6 7 Dishonest
    • Unfriendly 1 2 3 4 5 6 7 Friendly
    • Pleasant 1 2 3 4 5 6 7 Unpleasant
    • Selfish 1 2 3 4 5 6 7 Unselfish
    • Awful 1 2 3 4 5 6 7 Nice
    • Virtuous 1 2 3 4 5 6 7 Sinful

In an experiment that involved rating speakers, McCroskey (1966) found Hoyt reliability estimates for authoritativeness and character of .93 and .92, respectively. In testing construct validity, Carbone (1975) found that ratings of high- and low-credibility sources were significantly different and in the expected direction across the two dimensions.

Newspaper Credibility Index (Meyer, 1988)

  • Believability

    • Cant' be trusted 1 2 3 4 5 Can be trusted
    • Is inaccurate 1 2 3 4 5 Is accurate
    • Is unfair 1 2 3 4 5 Is Fair
    • Doesn't tell whole story 1 2 3 4 5 Tells the whole story
    • Is biased 1 2 3 4 5 Is unbiased

In modifying an existing index (Gaziano & McGrath, 1986) for measuring credibility of newspapers, Meyer (1988) developed scales for evaluating the dimensions of believability and community affiliation. West (1994) examined Gaziano and McGrath's and Meyer's scales and, consistent with the above introductory conceptual definition, found Meyer's adapted believability scale to have the strongest reliability (0.92) and the highest empirical validity.

McComas and Trumbo (2001) found potential utility of Myer's (1988) scale as a general credibility scale across source types. They used this scale in five environmental health-risk communication case studies to assess source credibility across the three source types of state public health department, local newspaper, and industry involved. The scale performed well both within and across the three source types, with an alpha of .83 across the five newspaper measurements, .86 across the five industry measurements, and .83 across the five state public health department measurements. The average alpha across all 15 indices was .84 with all values falling within the "good" to "very good" range.

Organizations as sources in health communication could include, for example, organizational communicators such as the Red Cross or the Centers for Disease Control and Prevention (CDC). Some research in this area has found consistency in dimensions with earlier credibility research, with organizational credibility including expertise and trustworthiness (and also attractiveness) (Metzger, Flanagin, Eyal, Lemus, & McCann, 2003). Web sites as sources also warrant specific mention in this age of consumer health informatics. Dimensions used in a scale to measure Web site credibility included the items of "trustworthy," "believable," "credible," "qualified," and "expert" (Dutta-Bergman, 2004).

Rationale for selection:

These scales were selected because of their widespread use and because they were tested for reliability and validity.

Additional Commentary:

The three scales included were developed using factor analyses of terms thought to at least in part represent source credibility. Criticisms of this approach include inadequate conceptualization of source credibility within the communication process, inadequate specification of measurement scales, and inadequate specification and definition of factors tested (Cronkhite & Liska, 1976; Delia, 1976; Infante, Parker, Clarke, Wilson, & Nathu, 1983). An alternative suggested by some is a functional approach, which assumes that perceiver evaluations of source credibility depend on the situation-specific function a source serves for a perceiver (Infante et al., 1983). Another situation-specific alternative is a constructivist approach which argues that individual construction of criteria, varying across "rhetorical situations," should be the premise and assumption used in credibility research (Delia, 1976).

Although much research exists on source credibility, including its measurement, a widely-endorsed single index that spans source types and communication situations was not found. McComas and Trumbo's (2001) findings for Meyer's scale are a step in that direction. Scales, including those above, as well as selected dimensions from scales, have been used and adapted to specific research.


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