The Science of Persuasion:<br/>Dimensions of Witness Credibility

The Science of Persuasion:
Dimensions of Witness Credibility

persuasion wit credThe term “witness credibility” is bandied about regularly in American jurisprudence. What are the factors that render a witness credible in the courtroom? In Chapter 6 of Persuasive Communication, my co-author and I assert that it is a witness’s level of expertise and trustworthiness that renders him or her credible. What’s more, it is important not only that witnesses possess these traits, but that the jurors and judges perceive witnesses as possessing those traits.1 That latter point cannot be underestimated. This paper addresses those factors that enable judge and jury to perceive that a witness is credible.

  • Source expertise is the extent to which a witness is knowledgeable about his or her topic. For fact finders to become convinced that a source is an expert, they must perceive that he or she possesses the appropriate knowledge, training, and/or experience concerning the topic at hand. For example, a hospital admissions clerk might be perceived by jurors as an expert on the process of admitting patients for scheduled surgeries. Jurors will be less likely, however, to perceive that clerk as knowledgeable about performance of the actual surgical procedures. On the other hand, a registered nurse may very likely be perceived as holding expertise in many areas related to patient care.
  • Source trustworthiness is, very simply, that speaker’s level of honesty and integrity. Unlike expertise, which is limited to a special subject area, trustworthiness is a general perception that transcends subject matter. Jurors and judges will form general perceptions concerning a witness’s integrity.

It is important to note that source expertise and source trustworthiness are distinct concepts, so that, for instance, a witness’s level of expertise might be vastly contrary to his level of honesty. The public’s perception that President Nixon was an expert on foreign diplomacy has largely remained unchanged over time, yet, by the time he left office, he was generally considered untrustworthy. In contrast, most people perceived that President Carter was honest, but they lacked confidence in his understanding of economic issues.

As mentioned, what should be of tantamount concern to those advocating in the courtroom is that jurors and judges perceive witnesses as possessing those characteristics of expertise and trustworthiness. Several factors will influence whether jurors and judges recognize that witnesses possess these traits. These factors include:

  • Fact-finder ability to understand the witness. The testimony a witness presents must be within the ken of the observer. An economist from MIT may have impeccable credentials, but if jurors cannot understand the substance of the testimony, they are likely to question the witness’s level of expertise. In contrast, an economist who has questionable credentials, but a knack for explaining economic concepts, may be perceived by jurors as having considerable expertise.
  • Fact-finder level of expertise. Individual jurors vary in the levels of education and expertise they possess. A juror who is a physician, for instance, may not ascribe the same level of expertise to a registered nurse who is testifying about standard of care. Someone outside the medical profession, however, may harbor no doubts about the nurse’s level of expertise.  
  • Fact-finder level of integrity. Similarly, jurors vary concerning their personal value systems and morality. While one juror might consider an act to be egregious, another might look upon that same act as “not a big deal.” For example, jurors who fudge the numbers on their tax returns might be less than critical of a real estate developer who failed to make full disclosures about a property’s history.
  • Witness likeability. A pleasant demeanor goes a long way in the courtroom, and is one very important factor that enhances perceptions of trustworthiness. Jurors generally find witnesses who are gracious, and willing to recognize and take responsibility for their own shortcomings, to be likeable and, thus, trustworthy.
  • Similarity between witness and factfinder.  When jurors perceive that a witness has membership similarity or attitudinal similarity, they tend to assign greater trustworthiness to that witness. Membership similarity is based on demographic and social characteristics, affiliations with clubs, groups, and organizations, and personal experiences that the witness has in common with jurors. Attitudinal similarity is the extent to which a witness expresses the same values, beliefs, and opinions that are held by jurors. People tend to trust others who hold their same opinions on important issues.2

The factors that enable judges and jurors to perceive witnesses as experts and trustworthy hold several implications for advocates in the courtroom. Attorneys must know their jurors. They must know jurors’ levels of education, so that they can coach witnesses to effectively relay information to these jurors. Lawyers must have some sense of each juror’s moral compass, and adjust their presentations accordingly. They must prepare witnesses to maintain composure and to behave in such a way that will evoke favorable sentiments from the jury. Finally, attorneys must elicit from witnesses aspects of their personalities, experiences, or lifestyles to which jurors can relate.




In August of 2016, Jim Stiff and Paul Mongeau published the third edition of Persuasive Communication. The book is a comprehensive review of the theory and research on persuasive communication that spans more than 80 years of academic work in the fields of communication and social psychology. This research note is part of a series that briefly discusses topics related to the science of persuasion. It describes the practical implications persuasive communication techniques offer to lawyers practicing their craft.


1. Hovland, C. I., Janis, I. L. & Kelley, H. H. (1953). Communication and persuasion. New Haven, CT: Yale University Press.

2. Simons, H. W., Berkowitz, N. N., & Moyer, R. J. (1970). Similarity, credibility, and attitude change: A review and a theory. Psychological Bulletin, 73, 1-16.

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The Science of Persuasion:<br/>Dimensions of Witness Credibility

Appeared in Persuasive Communication

May 31, 2017


James B. Stiff, Ph.D.

James B. Stiff, PhD, is the Jury Consultant Emeritus at IMS | The Focal Point. Dr. Stiff was the founder and principal of Trial Analysts, Inc. He received his PhD in Communication from Michigan State University in 1985, and was an award-winning professor at Michigan State University, Arizona State University, and the University of Kansas.

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