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What Makes Your Expert Witness the Best Witness? Social Science Research Highlights the Roles of Credibility and Influence

The adversarial nature of a jury trial leads many of our clients to ask, “Will my expert come across better than theirs?” This is a justifiable concern since jurors’ decisions about liability and damages often hinge almost entirely on the testimony and credibility of the expert witnesses.

Evaluating a potential expert based on credentials and experience provides only half the picture. Particularly when an expert is addressing a complex subject, jurors may have difficulty understanding the technicalities associated with their explanation and rely instead on heuristics—like credibility—for evaluating the testimony. In other words, the jurors rely on their opinion of the expert rather than the expert’s opinion. As a result, attorneys must attend to the expert’s projected credibility in addition to the content of that expert’s testimony.

Credibility is the foundational element that enables experts to successfully persuade jurors, and it has been the subject of social scientific research for decades. Over nearly thirty years, and through more than 20,000 cases and well over 1,000 trials, the world’s most influential litigators have trusted IMS to help identify, engage, and prepare best-aligned experts for their cases across nearly every industry and discipline. In recent years, social science research on credibility has illuminated key principles that we leverage to help our clients gain the best position to advance their cases and win.


Knowledge is a primary reason experts are called to testify; their expertise is supposed to be beyond reproach and ensures that their testimony informs the jurors. The domain of knowledge coalesces educational credentials, publications, and experience, each of which make an expert look great on paper. But an important part of knowledge is being able to deliver explanations with clarity, moderate assertiveness, and familiarity with the intricacies of the case. These latter factors serve to distinguish a good expert from a great one. Addressing each of these items during witness selection and preparation is critical to the success of a case presentation.

Experts may look great on paper yet shrink before the jury. An expert may be the preeminent authority in a particular field, but if they cannot clearly and simply explain key concepts to the jury, their persuasive power is lost. When an expert folds on cross-examination and fails to assert counterpoints, the jurors often believe the opposing counselors have “beaten” the expert and discount his or her testimony.

Not all experts take the time to ensure they can convey their knowledge. Some experts will fail to intimately learn the case, and they may hand the work off to an associate. Either in deposition or at trial, these experts lose credibility when they cannot command the facts in a way that coincides with attorneys’ case analyses.

The best way for expert witnesses to showcase the extent of their qualified knowledge is to act as teachers for the jury. Experts should be consistent and coherent, as they inform jurors on a concept. By demonstrating reasonable confidence in their own conclusions and opinions, experts should apply topical knowledge to their own case-specific knowledge.


Trustworthiness is a characteristic that is crucial to jurors’ decisions as to whether to believe or dismiss expert testimony. While jurors may recognize that experts are inherently biased—after all, each expert appears as either a “defense witness” or a “plaintiff witness” rather than a “neutral witness”—the extent to which jurors trust their testimony is tied to a number of factors.

For one, the above described perception of expertise is likely associated with perceived trustworthiness, as these factors tend to be quite interrelated. An expert who comes across as a patient, but authoritative teacher is likely to be perceived as quite trustworthy.

Second, an expert’s demeanor on the stand influences jurors’ evaluation of trustworthiness. There are nonverbal cues that are traditionally thought to be indicative of honesty or dishonesty. For example, one study found that an expert witness’ ability to maintain eye contact with both the attorneys and jurors was predictive of credibility ratings.

Third, empirical research has shown that the number of times an expert has testified and their compensation are both associated with perceptions of believability—also known as the “hired gun effect.” Often this effect arises when there is a significant disparity between the amounts opposing experts are compensated. For instance, jurors may be suspicious of an expert in an antitrust case who receives $300,000, while the opposing expert is paid $30,000. To combat jurors’ perceptions that a higher paid witness is simply a hired gun, the witness’s testimony must assure jurors that payment is merited due to the witness’s exceptional level of expertise.


Many experts are asked to expound upon complex and arcane concepts which may be confounded by industry or technical jargon, and which could be difficult for juror laypersons to comprehend. In these instances, jurors rely on heuristic cues like credibility to guide their evaluation of the testimony. An expert witness may endear themselves to a jury by using simple terms or metaphors, by integrating demonstratives, and by remaining patient and steadfast during cross examination.

An effective expert is not merely perceived as a trustworthy intellect, but as someone who is considerate enough to take the time to convey their knowledge in ways the audience can understand. An expert’s dynamism, coupled with display of their deep passion for and mastery of the subject matter, will frequently carry the day.


Finally, there is the rather broad question of whether an expert is likeable. It is indeed rare that a knowledgeable, trustworthy, and dynamic witness will be unlikeable, but most lawyers have encountered at least one expert who comes across abrasively – or even with an air of arrogance. Likability has been found to be tied to both perceptions of trustworthiness and credibility as a whole, according to “Credibility in the Courtroom: How Likeable Should An Expert Witness be?

Many attorneys have experienced a sinking feeling while watching jurors react negatively to an expert who offers a sarcastic response during cross examination. The expert witness who is disliked by a jury will torpedo their own testimony. While jurors might believe the expert is very competent and knowledgeable, they may discount – or even dismiss - the testimony on the basis of their dislike for the expert. Worse still, they may channel this dislike to the party that the expert represents. Jurors assess the likability of witnesses based upon their friendliness; the level of respect they show to the parties, the jury, and the court; their ability to use informal language; and the various nonverbal behaviors they exhibit, like eye contact and vocal inflection.

© Copyright 2002-2022 IMS Consulting & Expert Services, All Rights Reserved.National Law Review, Volume X, Number 222

About this Author

Clint Townson Litigation Consultant IMS Consulting & Expert Services
Associate Jury Consultant

The nation’s leading litigators rely on Clint Townson, Strategy Consultant, to meticulously design and execute mock trials, focus groups, and community attitude surveys that yield reliable data to guide the development of their high-stakes cases. His background in communication informs theoretically grounded strategic recommendations that have helped attorneys in Am Law 200 firms achieve winning case outcomes. Clint’s graduate education and experience utilizing a variety of the world’s most advanced research methods and statistical analysis techniques have equipped him to develop...