Experts know things. That’s what makes them experts. That is why they’re allowed in court: to inform the jury’s or judge’s understanding. Once there, of course, they are picked apart by an adversary with the goal of making them look wrong or foolish. In that context, a defensive feeling can kick in:Don’t give an inch…Don’t show any weakness…Don’t admit to any uncertainties or gaps in knowledge that could be used against you…. Litigators and experienced experts know that this attitude can lead a witness onto thin ice, and can tempt one to make a false or exaggerated claim that damages the expert’s credibility far more than an honest “I don’t know” would have. In addition, the pressure to know everything is often, and appropriately, at odds with an expert’s scientific training. After all, there’s the saying that “An expert is someone who knows what they don’t know.” There is a role for imperfection and uncertainty, and based on the scientific tradition, it is a pretty important role.

In a recent article in Scientific American, for example, genetic researcher Jim Kozubek writes that science does not exist in some kind of timeless bubble, but instead is susceptible to the limitations and plot imperfections that affect other stories. I think the story framework is useful for scientists, including experts in court, because it captures the need for coherence — a “hanging together” of the narrative — while also capturing the essential incompleteness. A story is rarely or never built on universal knowledge. Rather it is a perspective, and so is testimony. Hopefully, it is a good and useful perspective, and hopefully it is a perspective that is better than the adversary’s. But it is a perspective nonetheless. In this post, I share a few reminders on when the testifying expert should gain some credibility by admitting to not knowing everything.

Admit It…

When Your Story Is Limited by Your Source Material

Testifying experts are unique compared to scientists and other academics in the sense that they are not fully in charge of their own source material. Typically, they aren’t running an independent investigation of the questions at hand. Rather, they are reviewing what counsel gives them, and rendering an opinion that is limited to that. Generally, that source material is pretty complete, but occasionally — either because counsel is trying to economize or trying to be too clever — that source material is lacking something. When that happens, the expert is best off admitting it, without throwing the client under the bus, but without requiring opposing counsel to wring it out of them either.

I believe that I conducted a thorough review and have a strong basis for my opinion based on what I reviewed. But, if there are details not included in that review, I am obviously not going to be the one to offer an opinion on those details.

When Your Story Contains Some False Leads

Experts go to great lengths not to make any mistakes in the testimony they are offering to the other side, or to a judge or jury. Still, it is a long road through discovery, and the factual landscape of a case can be changeable. From the expert report, through the deposition, and into trial testimony, inconsistencies or gaps can crop up. And on some occasions, an honest expert will be forced to admit that an earlier statement is wrong. Again, the best advice is to be straightforward and to not let the other side make a chase out of it:

My goal is to make my opinions and the bases for them as clear as possible, and to make everything accurate for the jury. So if there is anything I am offering that is wrong or could be taken the wrong way, that needs to be corrected. In this case, that earlier statement is false. It is false because I did not have the complete picture at the time, but it is still on me to correct it, so that is what I am doing. The correct statement is…

When Your Story Doesn’t Have an Ending

Sometimes, the main question that a jury will be wondering about is a question that the expert cannot fully answer. They have an opinion where it legally matters, but they don’t have the complete answer that the jury is looking for, often because it cannot be known. For example, the expert in a medical products case might be clear in testifying that the company’s drug did not cause Mr. Smith’s heart attack, but not able to offer an opinion on what did cause the heart attack. In a case like that, the testimony might be legally appropriate, but still not psychologically satisfying: It exonerates one suspect, but without answering the central “Who done it?” The best an expert can do in a situation like that is to focus on the relevance of what is known, and try to de-emphasize the relevance of what isn’t known.

In my testimony, I really wish that I could answer everything that is on the jury’s mind. Unfortunately, I cannot do that today, because there are some things that, based on the state of medicine and the state of the facts, we really cannot know. Fortunately, I believe that I can help this jury answer the question that the law is putting to them today. And that question is whether the drug caused the harm to Mr. Smith. That is the right question because, out of all the conceivable causes of Mr. Smith’s heart attack, only one is on trial today. So I can speak to that factor, and confidently say that the product did not cause the heart attack.