Expert Witness Credibility Model ForensisGroup BlogUndoubtedly, the knowledge that an expert witness has and conveys during testimony has a direct relationship to an expert’s credibility with juries. However, an expert’s level of knowledge does not, in itself, necessarily correlate with credibility. In fact, some jurors have reported feeling alienated by some experts who seem to be so-called “hired guns.” This article examines juror perceptions of expert witness behaviors, highlighting the findings of a study that put these factors to the test in mock juror, research, and other clinical/legal settings.


The American Academy of Psychiatry Law (AAPL) recently conducted a study to determine the effect of an expert witness’s speech and actions on jurors and the implications for that expert’s credibility. See Caroline T. Parrott et al., “Differences in Expert Witness Knowledge: Do Mock Jurors Notice and Does It Matter?” J. Am. Acad. Psychiatry Law 43:69 – 81 (Nov. 1, 2015). On the one hand, as the study explains, “the court’s sanction of a witness as an expert” as being reliable enough to testify under the rules of evidence gives experts a certain level of credibility. Id. at 69. However, “a witness’s expert status has the potential to backfire and create distrust in the form of skepticism that the expert is a hired gun or feelings of comparative inferiority on the part of the trier of fact.” Id. Accordingly, it is important to evaluate the effects of expert behavior and the ways that juries perceive experts to determine what displays of knowledge and types of testimony are most effective at building credibility with jurors and succeeding in court.

Without question, an expert who is seen as credible by jurors has a powerful ability to sway a verdict and generate a successful outcome for a particular case. See id. The AAPL argues that “Expert witness credibility has been instrumental in verdicts…in both criminal trials and civil proceedings with mock, potential, and real jurors.” Id. at 69-70.

The AAPL authors have created a four-part framework for evaluating the credibility of an expert on a court, called the Witness Credibility Model (WCM). See id. at 70, citing Brodsky, Griffin, & Cramer, “The Witness Credibility Scale: an outcome measure for expert witness research,” Behav. Sci. & Law 28:892–907 (2010). The four components that the authors consider key to establishing such credibility are confidence, likeability, knowledge, and trustworthiness. Id. The first three components are discussed herein, but trustworthiness is not, because the AAPL study explains that the term has not been “operationally defined” and researched within the context of the WCM. See id.

(1). What a Confident Expert Should Look Like: The authors define expert confidence as “The degree of demonstrable self-assurance expert witnesses have in their general ability on the stand,” and the perception of expert confidence is a component of how credible a jury finds that expert. See id. The AAPL study breaks down confidence regarding how an expert is perceived by jurors into three categories: low, medium, and high. See id. at 71.

An expert who is seen as having low confidence might testify in a “quivering tone of voice,” have “dysfluencies in speech” (e.g.-speech that is not smooth, has inappropriate pauses, or contains repetitious words or syllables), and/or vacillate or greatly vary the pace of their speech. See id. Other signs of low confidence are awkward posture, repeated corrections made in testimony, and eye contact that is fixed in one particular place or at one particular person(s) (or no eye contact at all). See id. Two ways in which an expert witness’s language reflects low confidence are seeking reassurance from a questioner by making statements such as “you know,” and asking (often multiple times) for a question to be repeated. See id. One last way in which low confidence is projected is by a witness having outward signs of anxiety or nervousness. See id.

The authors found it important to differentiate between medium/moderate confidence and high confidence in expert testimony, which can be of great use to attorneys who select and coach their witnesses. The difference between an expert who projects medium confidence versus one who comes off as having a high level of confidence can be the difference between a jury feeling ambivalent about an expert and being completely swayed by that witness.

Experts who appear to have a medium level of confidence often have clarity in their speech and have moderately paced speech as well. Id. They may also have a moderate, stable tone of voice. See id. One simple way to discern whether an expert has medium (instead of high) confidence is in the way the witness answers certain questions. An expert with medium confidence will have a moderate degree of certainty on an issue, and may say things such as “I am reasonably certain” about a particular issue. Id. A moderately confident witness may make smooth statements and tell coherent stories, and that individual may also have good posture. See id. To project a medium level of confidence, an expert may appear somewhat calm and poised, seem comfortable testifying, and be able to provide appropriate responses to questions. See id. In addition, a moderately confident expert witness will tend to have consistent eye contact and will not generally ask to have a question repeated. See id.

In contrast, expert witnesses who convey high confidence behave in more assertive manners. One way in which an expert demonstrates high confidence is through a loud, strong tone of voice and through speech and mannerisms that appear assertive in court. See id. Experts who speak rapidly also impress a high level of confidence upon juries. See id. Another component of high confidence is linguistic: experts using always and/or all statements, such as “I am certain” in response to a question are seen as highly confident. See id. Some final components of high confidence include good posture, coupled with leaning forward (this may demonstrate an eagerness to impart knowledge and/or interest in the subject under discussion) and speech that is highly fluent. See id.

(2). What a Likable Expert Should Look Like: According to the authors, the second component of witness credibility—likeability—is defined as “The degree to which an expert is friendly, respectful, kind, well-mannered, and pleasant.” Id.

Experts with a high level of likeability will take care in the words they choose to express something. Specifically, highly likeable witnesses will consistently use the words “’we’ or ‘us’ when discussing members of the scientific community or humanity as a whole.” Id. Highly likeable experts will also smile from time to time and will maintain consistent eye contact with lawyers and jurors. See id. Moreover, to have a high level of likeability, an expert witness will speak somewhat informally, limiting their technical jargon or, for example, will refer to the litigants by their last names (e.g.,-“Ms. Jones,” “Dr. Roberts”). See id.

Expert witnesses with a low level of likeability demonstrate different traits. They tend not to use the words “we” or “us,” which can cause jurors to feel that they are not united with the witness or that the witness feels superior to others. See id. Moreover, failing to smile at all and/or not making eye contact (or inconsistently doing so) are indicators of low likeability. See id. Other behaviors associated with low likeability include: excessively stating the certainty of one’s conclusions and using highly technical (and therefore, inaccessible) jargon. See id. Finally, frequently referencing the parties formally (e.g.- “the client,” “the defendant”) is a behavior associated with low likeability of experts. See id.

(3). What a Knowledgeable Expert Should Look Like:  The third component of expert credibility is knowledge, which the authors define as “[t]he degree to which an expert is perceived to be well informed, competent, or perceptive and to possess or exhibit intelligence, insight, understanding, or expertise.” Id. at 71.

The study expressed that experts can be considered to have low or high knowledge by jurors. Experts who possess strong educational credentials, such as being board-certified in a particular area, and/or who have written a number of academic publications in areas of expertise that pertain to a specific case, fall into the high knowledge category. Id. Expert witnesses who have strong clinical and/or research experience about the particular issue being tried in a case also fall into the high knowledge group. Id. In addition, experts who are consistently clear (and easy to comprehend) and whose communication to a jury is primarily of a substantive nature are perceived as being highly knowledgeable. See id. Another way that an expert can be regarded as being highly knowledgeable is by being moderately assertive (but not aggressive), using language such as, “As far as I know, I’ve never been wrong,” when they are questioned about their awareness of clinical errors. Id. The study also found that self-proclaimed expertise can be helpful as a form of high knowledge and that witnesses who make statements such as “In my expert opinion…” are seen as credible by jurors. Id.  The final source of high knowledge that the study discusses is demonstrations of familiarity with a case or issue by an expert, which can be established by the expert mentioning the multiple interviews that they have had with one of the litigants, for example. See id.

The authors also express what expert behaviors are perceived to be low knowledge. An expert who is seen as having a low level of knowledge may commit errors, such as not mentioning their educational credentials or having little to no experience on the particular issue they are testifying about. See id. Witnesses who have inconsistent clarity or who focus on superficial, rather than substantive, communication also fall into the low knowledge category. Id. Experts with low assertiveness levels (e.g.-answering “no” when asked if they are aware of possible clinical/clinician error) are also considered by juries to have low knowledge. Id. Finally, two other behaviors fall into the low knowledge category: experts who lack self-proclaimed knowledge, and experts who lack adequate familiarity with a particular case (for example, an expert who has only met with a litigant one time very close to the trial date). See id.


Expert witnesses have a variety of characteristics that they exhibit while testifying, and each of these characteristics can play a role in a jury’s decision regarding whether a particular expert is credible. The WCM model, as explained by the guidelines above, provides attorneys with the opportunity to vet their experts and determine how these witnesses will be perceived in court. Moreover, using the above criteria, attorneys can train their expert witnesses by playing up certain behaviors that are well-received by jurors and eliminating others that are not. In so doing, attorneys and their witnesses can discover the best ways to ensure that their arguments are the most persuasive and, ultimately, the most successful.


By: Kat S. Hatziavramidis, Attorney-at-Law

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