Conventional wisdom holds that jurors don’t trust expert witnesses because they perceive them to be…well, adjunct practitioners of the world’s oldest profession. While it may be true that many people profess this attitude about expert witnesses in the abstract, that cynicism all but disappears when people are sworn as jurors and are then charged with deciding a defendant’s fate. In these concrete circumstances, jurors find themselves looking for all the help they can get. They also quickly realize that one of the best sources of that help is the expert witness.

The more complex and technical the case, the more jurors rely on experts to help them understand case facts and issues. In turn, one of the primary metrics jurors use to judge an expert witness is their evaluation of the witnesses’ credibility.

Simply put, credible experts influence jurors positively about the merits of your case.

So...

How can you tell if jurors are likely to see your expert witness as credible?
How do you begin applying some level of objectivity to your witness evaluations?
What signs should you look at as you evaluate your expert’s performance?

Research on expert witness credibility by Dr. Stanley Brodsky of the University of Alabama offers some hints. The research of Brodsky and colleagues (Brodsky, Griffin & Cramer; 2010) indicates that jurors’ perception of an expert witnesses’ credibility has four primary components. They are listed here in descending order of importance:

Confidence. Does the witness demonstrate reasonable confidence in their opinions?
Trustworthiness. Does the witness inspire trust?
Likeability. Do jurors find the witness likeable?
Knowledge. Does the witness seem informed?

Brodsky’s findings suggest that the component confidence accounts for about 50% of expert witness credibility, trustworthiness for about 9%, likeability about 7%, and knowledge about 5%. Taken together, these components account for nearly 70% of a witness’ credibility with jurors.

By keeping these four components in mind as you evaluate your witness, you can begin to give yourself a more objective sense of jurors’ likely reaction to your witness, and help yourself isolate the areas you need to focus on during witness preparation.

If your evaluation reveals that your witness has a problem with likeability, then you’re probably in pretty good shape, since likeability is only 7% of credibility. But, if you find that they seem to have a confidence problem (about 50% of credibility), then you should probably plan to spend some more time with them, or, start looking for another witness.

A note about Confidence

In this context, the components of trustworthiness, likeability and knowledge are all pretty much self-explanatory. But confidence is slightly different. Jurors set different confidence expectations for fact witnesses and expert witnesses. They expect fact witnesses to be highly confident, while they expect expert witnesses to be reasonably confident in their opinions. Jurors, it seems, recognize a sort of “sweet spot” for expert opinions and are suspicious of highly confident opinions from people who, like themselves, weren’t actually there. Consequently, jurors give better confidence ratings to experts who are “reasonably confident” in their opinions than they do to experts who are either “highly confident” or “slightly confident” in their opinions.

Brodsky, S. L., Griffin, M. P., & Cramer, R. J. (2010). The Witness Credibility Scale: An outcome measure for expert witness research. Behavioral Sciences & the Law, 28, 892–907.