Expertise About the Experts

A litigator’s guide to vetting scientific experts

Made famous by films such as “The Verdict” and “My Cousin Vinny,” expert witness testimony brings to mind people with advanced degrees who use esoteric industry jargon. 

But experts testify to help juries understand complex issues in cases, including in personal injury law. But where one side of a case brings in an expert witness, there’s an opposing attorney doing his or her own vetting to make sure the expert’s testimony belongs.

Experts such as accident reconstructionists and those who testify about soft tissue injuries impossible to see, such as to the brain or spine, tend to be among the most hotly contested. In the past, courts tended to trust experts who gave opinions based on generally accepted scientific knowledge. But in recent years, the focus has turned to how rigorously experts apply the scientific method when they form opinions. Regardless of whether they represent plaintiffs or defendants, personal injury attorneys seem to agree that if an expert backs his or her opinions with a solidly grounded scientific method, their testimony will stand up to the toughest of examinations.

“Once you get that answer, there is no antidote to them,” said injury and wrongful death attorney Larry Cohen during a CLE presentation last Tuesday on guidance for gathering scientific evidence in cases. “They will give you what you need.”

Red Flags

Wheeler Trigg O’Donnell partner Craig May, who has defended personal injury cases, said a judge can make the call about whether an expert witness’ testimony is really adding anything to the case in deciding whether to admit it. As an example, he said he has read about cases involving falls that have called experts to testify how a floor became slippery.

“A jury can understand a slippery floor,” May said. “And they may not need an expert to explain to them” that concept. He said such situations where the testimony is not truly expertise is a red flag to look for when determining if a court should admit it. 

Personal injury plaintiff attorney Tom Metier said attorneys will sometimes hire an expert because of his or her résumé, such as an Ivy League degree, to make his or her testimony sound all the more impressive, instead of focusing on the quality of the opinion they offer.

“Science doesn’t live only at the Ivy League,” Metier said. “What makes them a world-class expert is the quality of their work and experience.” He said an attorney can look at the his or her publications and history as an expert witness, such as how they’ve testified in the past and the quality of their investigations, to determine how well they could serve in a case.

“If (testimony) is not based on good, defensible rigorous science and input,” May said, “Garbage in, garbage out.” He explained that while scrutiny of expert witnesses in the past has looked at whether they testify using generally accepted science, because courts typically do not welcome the use of unestablished theories, the 1993 U.S. Supreme Court decision in Daubert v. Merrell Dow Pharmaceuticals put focus on whether experts apply a rigorous methodology to their opinions and that judges should be able to assess that methodology and the facts.

“What if [an opinion is] generally accepted, but based on bad science?” May said. “Well, then that shouldn’t come in.”

A Toolkit for Examination

During his presentation, Cohen laid out a framework of questions for attorneys to ask when examining an expert witness  who is giving any kind of scientific opinion to help decide whether his or her testimony should be admitted.

Validity: Does the analytical instrument an expert used to help form his opinion measure what it purports to?

Cohen used the example of a bathroom scale. “Someone says a bathroom scale works because I can stand on it and it tells me my weight,” he said. “How do you know? Somewhere in time, somebody had to do some research to figure out how the bathroom scale works, such that it could tell us weight, and make the determination that it works.”

Reliability: Does the instrument measure consistently?

Cohen explained reliability in this context differs from legal reliability for admitting scientific evidence. He said a person can examine reliability by looking at how an instrument was developed and its claims about the extent of its validity.

“You aren’t going to find things out there that are valid and reliable 100 percent,” he said. “The difference between the reality that’s out there that we’re trying to identify and the conclusion that we can draw using these instruments is referred to as a rate of error.”

Sensitivity: How correctly can the instrument identify people with the condition it measures?

“If it’s valid and reliable but not sensitive, we’re back to the question of what usefulness this has in supporting an opinion,” Cohen said. “If (the expert) says ‘I don’t know,’ what’s the next step? A motion in limine to eliminate that opinion, because they can’t support it.”

Specificity: Can the instrument identify the absence of the condition, and rule out other explanations?

Cohen used the example of a person who appears to have a short-term memory problem but an alternate explanation might be an attention issue that prevents him or her absorbing information. 

“The instrument that you want to say detects short-term memory, is it specific to that, or is it also picking up attention?” he said.

“These are questions you can always ask, and they will always lead you to things that you can use on direct and cross-examination.”

— Julia Cardi

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