Expert Witness Credibility: What Factors Influence Perception?

Carolyn Casey, J.D.

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— Updated on June 21, 2021

Expert Witness Credibility: What Factors Influence Perception?

Expert witness credibility can make or break legal cases. Your expert witness must be credible in the eyes of two audiences: the judge and the jury. Lawsuits frequently depend on how juries interpret expert witness technical or industry standards testimony. A judge’s perception of expert witnesses and their testimony is also extremely critical. A party can move to exclude an expert’s testimony, asking the judge to determine the witness is not credible under the Daubert standard.

How can you know in advance if juries and judges will see your expert as credible? Here are five factors worth considering when selecting your next expert witness. The guideposts address personal impressions, federal rules, and precedents concerning expert witness credibility.

Subject Matter and Case Expert

First off, find an expert with the knowledge and experience to speak with authority on your case’s issues. As the witness proponent, it’s your job to communicate the expert’s credentials, education, specialties, publications, and experience to establish their qualifications and credibility. As you read their CV, ask yourself how a judge a jury will view this expert’s credibility.

Less obvious is the need to ensure that your expert knows your case. It’s imperative that your expert study the case facts, records, and materials. The witness may be a renowned expert in the exact medical specialty you need, but if they didn’t read your case medical records, they can easily be tripped up by your opponent. Appearing to opine without knowing the facts of the case will plummet witness credibility. Judges have been known to throw out expert witness testimony when it is clear the expert lacks familiarity with case medical records.

Dig Into Red Flags For Potential Bias

Be sure to dig into any potential bias a jury or judge may perceive in your witness.  For example, if your expert provided consulting services to your client 10 years ago, you’ll want to know that and keep looking for another expert. A reasonable juror would perceive that this witness is likely biased in favor of your client, and therefore discount their testimony. When bias is observed, loss of credibility quickly follows.

Moreover, a judge can determine that an expert was swayed by evidence, injury, or the client, and disqualify that witness from submitting a report.

Demeanor and Etiquette

Though it’s easy to assume a learned expert understands basic courtesy and how to present themselves in court, you’d be surprised. Coach your expert on how the judge and jury will perceive them based on body language, dress, and etiquette. Don’t take anything for granted or hesitate to convey even things that seem obvious.

  • Seasoned litigators advise experts, “Dress appropriately. Come to court clean, well-groomed, and conservatively dressed. Stick with formal job interview clothing to the best of your ability. Wear dress pants, collared shirts, conservative blouses, and dresses/skirts that fall at a professional length.”
  • On personal habits and communication style, these same litigators say experts must appear respectful. “Court is not the forum for speaking out of turn, laughing uncontrollably, or using slang terms or complex jargon. Wait patiently until you are called to the stand before you say anything about the case. Do not chew gum.”
  • The Journal of the American Academy of Psychiatry and the Law found that extraversion—as measured by expressiveness in face, movement, and voice—made jurors perceive expert witnesses as more likeable. However, likeability’s impact on credibility varies depending on the perceiver. The study found that extraverted jurors tend to see witnesses they like as more credible. Yet, introverted jurors’ perception of witness credibility was not influenced by their likeability.

Solid Methodology

Federal Rule of Evidence 702 codifies the Daubert ruling, which broadened the judge’s role in assessing the admissibility of expert witness testimony. Today, judges must determine if an expert’s methodology is sufficiently reliable to support the opinion provided.

To avoid credibility hits and even disqualification problems, ask your expert to walk you through their methodology. Let them know you like to make sure their methods will hold up if challenged in court.  Listen for any gaps or common-sense indicators that something is wonky. Further, ask them if others in the field use this same approach or if this is novel.

Just The Facts, Mr. Expert

The last thing you want is to have your expert’s testimony excluded because they strayed into the province of the judge. As the ABA explains, under Federal Rule of Evidence 704(a), expert witnesses may offer testimony on factual issues that a jury will decide as the “trier of facts.” They cannot, however, render legal opinions or advise a jury on the law. They must not even dance close to the edge by asserting what law applies in this case or inferring that a defendant violated the relevant law. This is the sole arena of the judge, who will kick your expert testimony out if he or she perceives a whiff of legal opinion in the expert’s testimony.

Apply these perception factors when selecting and preparing your next expert witnesses. This will ensure smooth sailing on your expert’s credibility perception.

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