An interesting article adaptation from an original work by Laurie R. Kuslansky, Ph.D., with additional comments by myself:
Expert witnesses, if they are well prepared and know your case well, can go a long way to helping you win your case at trial. Often, a case will center on an engineering, scientific, environmental, or similar issue, and having the right expert can make all the difference.
However, the flip side is that a poorly prepared expert witness, or one who does not testify effectively, can help you lose your case.
Here are seven things that your expert witness should never say.
“That’s not my field of expertise, but …”
The classic mistake an expert can make is to wander outside his or her area of knowledge and expertise. An expert should never sound evasive or ill-informed. If the answer to a question on cross-examination is truly outside his or her field, it’s not relevant to his or her direct testimony, or the question should draw an objection, the best way for an expert to be believed about what they do know is to admit what they don’t know when it isn’t in their domain. If it’s relevant, the expert should be prepared and should answer.
In one case, I was “taken on” because I used the words “Causal link.” It turns out the Magistrate believed that this is a “legal word” and should only be used by people qualified in law. This was “so serious” that it was brought up in judgement.
“I have no idea.”
Again, don’t sound evasive or ill-informed. A better answer is, “Under the assumptions that I am making, which are …, here is what I’d expect to happen.” In addition, the expert should explain why it is not relevant.
If I am confronted with an issue, I have no answer for, I always answer honestly. I’d rather be known as being “honest” than always “fighting to be right.” This is the realm of attorneys. As the saying goes: Attorneys at law will do anything to win – even tell the truth…
“I said that in my report, but …”
Do not back down from the report and create uncertainty. The report should be carefully crafted to embody the expert’s conclusions. A significant weakness for any witness is to reverse positions. If for some reason, such as new information that was not available when the report was prepared, became known to the expert, then it should be made clear that the report was based on what was known at the time. Otherwise, there are better ways to explain apparent inconsistencies. Cross examination is likely to exaggerate such points and it is the expert’s job to neutralize them and put them into better perspective.
This is why I prefer to be present during as much of the trial as possible or to see transcripts of evidence led, where possible. There is nothing worse than having an opinion that forms the essence of your “expert opinion” only to find that your point of departure was inherently flawed.
In one case an opposing expert had estimated the “turning radius” of a road at 250 m (about 820 ft). He completed his calculation and based his findings on 200 and 250 m (656 and 820 ft) “to allow for error.” I measured the same road with a Laser Total Station. The radius was ACTUALLY 90 m (295 ft). When confronted with this in court, during testimony – the expert exclaimed “Phew! Then I was very wrong!” That was the end of that…. We won the case and the judgment was rather negative about the expert. It included that “he did not help the court.”
“I changed my mind.”
Again, this creates a dangerous amount of uncertainty for the trier/s of fact and leads them not to rely on an expert as an expert. If the expert really needs to modify some aspect of his or her testimony, tackle that directly by explaining in open court what slight change is needed and why.
If you have all the proper evidence, the chances of this happening is proportionately reduced. This is why our investigations are typically designed to gather all the available evidence possible.
“I could be wrong, but …”
The expert should never make this concession. The expert’s job is to be forceful and help the trier’s of fact. The trier/s of fact may discount part of the expert’s testimony, but his or her job is not to help them do this. Such type of humility does not serve an expert well.
This is an expression that is more a “figure of speech” than an actual admission. But we’re talking court here, so “everything you say can and will be used against you.” In court you should “speak less and say more.” Period.
“I’m not really an expert.”
Then why are you on the stand? Under the law, expert testimony is admissible only if the expert is qualified, if his or her testimony will help the trier/s of fact decide issues in the case or understand the evidence, and if the expert’s testimony is based on sufficient facts or data, is the product of reliable methods and principles, and if the expert has reliably applied the methods and principles to the facts of the case. Otherwise, the expert shouldn’t be on the stand. If an expert is unwilling to make a firm commitment to an opinion and to their area of expertise, do not risk putting them on the stand. This is especially relevant when using an expert without enough experience testifying.
In a matter I testified in, a Metallurgical Expert confessed this very thing when asked if he examined the roadside barriers at a crash scene. He was asked (several times) why he did not examine them. It then went to “but these things are metal. You are a metallurgical engineer, and you are saying you don’t know anything about things that are actually metal?” He replied (feebly) with: “I am not a barrier expert.“
“The lawyers told me to say that.”
No. Although the expert is on your side, he or she is not a mouthpiece for the lawyers. He or she has objective expertise based on science and technology and has composed an independent opinion. It is up to the expert to own it.
This is easy to say, but there are cases where attorneys INSIST that certain aspects of your report should be “left out.” This is a problem, since it is my experience that these “silent killers” can assassinate your evidence in very short order – and your credibility along with it. I rather lose clients or walk away from cases than “cook the books” with regards to evidence.