Cross-Examining Expert Witnesses: Foundational Attacks

Ginni Chen, J.D.

Written by
— Updated on February 12, 2021

Cross-Examining Expert Witnesses: Foundational Attacks

When it comes to cross-examining the opposing expert witness at trial, keep in mind what the late Muhammad Ali once said, “The fight is won or lost far away from witnesses – behind the lines, in the gym, and out there on the road, long before I dance under those lights.”. It’s how you prepare that determines the outcome. These words are as true of boxing as they are of trials – especially when it comes to expert witnesses.

When it comes to cross-examination, preparation at the deposition and discovery stage is key to undermining an expert’s testimony. You’ll want to know exactly what the opposing expert witness intends to say in court, what he/she is basing their opinions on, and what conclusions they’ve drawn. Be sure to conclude the deposition by asking if there are any other opinions that the opposing expert intends to express at trial – it’s a good way to avoid any undue surprise at the trial stage.

Once you know the exact substance of the expert’s testimony, you’ll want to analyze all the information that both supports and undercuts the opposing expert’s opinion. Be sure to closely review and scrutinize the expert’s report, with an eye to every single error or inconsistency. When you have a complete and thorough understanding of both the expert’s testimony and report, you can start to identify some of the foundational weaknesses outlined below, and build an effective cross-examination strategy around them.

In a foundational attack, your cross-examination should chiefly exploit the following areas:

  1. the opposing expert’s investigation of the case at hand,
  2. the opposing expert’s methodology, and
  3. the opposing expert’s conclusions.

There are several ways to approach weaknesses in each of these areas. Which ones you choose to use will depend on the idiosyncrasies of your case and the opposing expert.

1) Challenging the Expert’s Investigation

To challenge the expert’s investigation of the case, you can exploit deficiencies in the opposing expert’s understanding of the facts. Or you can highlight problems with the how the investigation was conducted.

The former requires disputing the facts on which the opposing expert’s opinion is based. It’s perhaps the most direct way to encourage the jury to disregard the expert’s testimony; since an opinion is only as good as the facts on which it is founded. Show that the expert had insufficient or inaccurate facts and data for his or her investigation. If the expert used a simulation, show that the simulation differed, significantly and meaningfully, from the real world facts in the matter at hand.

One of the benefits of attacking the facts of the opposing expert’s opinion is that it lets you stay on familiar ground during cross examination, since you already know the facts inside out. Additionally, you can avoid getting mired in a complex argument about the science; which can be a potentially confusing line of questioning for the jury.

Alternatively, if you can’t challenge the facts, you can challenge the investigation itself. You will want to exploit any differences between the opposing expert’s investigation and standard procedures by asking questions that compare his or her investigation against model investigatory protocol. Be sure to highlight investigatory measures that might have been more appropriate for the case at hand that the expert did not follow.

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One effective way to structure a cross-examination is to ask the expert for their opinion on what a “good investigator” might do. Then list your suggestions for a model investigation. This should lead them to agree with all of your suggestions. For example, you would phrase multiple questions as, “do you agree that a good investigator would do X, Y, and Z?” with the opposing expert assenting in response. You will then be able to highlight that the opposing expert didn’t do that by following up with, “But you didn’t do X, or Y, or Z, did you?” On the one hand, you are having the opposing expert agree with you on what best practices would have been. While on the other, you are demonstrating that the expert fell short of these best practices and thereby compromised the investigation.

2) Challenging the Expert’s Methodology

If you’ve done your homework into the expert’s field, you may be able to call the expert’s methodology into question on cross. If the expert’s methodology is incorrect or not generally accepted in their field, you will want to underscore that point thoroughly. If the expert’s methodology is generally accepted by the scientific community, you’ll want to identify instances where the expert may have strayed from standard procedure. And if the expert deviated from scientific protocols mandated by legislative, regulatory, or scientific authorities, you will certainly want to explore that point during cross-examination.

Even if the expert did follow mandated scientific procedure, they may have executed the procedure in a way that would distort the results. If, thereafter, the opposing expert did not properly qualify the results, you will want to bring this to light during cross-examination.

On the subject of skewed results, it may also be worth questioning the expert about the funding of their study, test, or investigation. Most likely the procedure was funded by opposing counsel, or by firms with a vested interest in a particular result. This may be worth pointing out to the jury as they consider the reliability of results.

3) Challenging the Expert’s Conclusions

When challenging the opposing expert’s conclusions, consider whether the expert is basing their conclusion on a specific scientific test, or whether the expert is relying on their generalized experience, research, and knowledge.

If the expert is relying on the results of a specific scientific test; you will want to demonstrate that either the expert’s conclusion, or the test result on which it is based, is not generally accepted in the expert’s peer community. If the tests, results, and/or conclusions have previously been excluded by other courts; you will want to delve further into their exclusion on cross.

You will also want to highlight on cross-examination if no other scientists in the expert’s field have gotten similar results or reached the same conclusions. If the scientific results are a statistical anomaly among a multitude of similar tests, you may want to hone in on that fact as well. It may be particularly helpful to point out that independent researchers have not obtained similar test results or reached the same conclusions. Thus suggesting that the expert’s anomalous conclusions may be a product of faulty scientific reasoning as well as bias.

To elaborate, let’s say the expert testifies that he or she concludes X because a specific scientific test show Y. This conclusion could allow you to exploit a number of weaknesses. First, you could show that the expert’s community generally reject tests that show Y.  Second, you could show that the expert community generally rejects the assumption of X because of Y, or even that they generally reject ever concluding X at all. You could thereafter show that all others in the expert’s field, including independent researchers, conclude A instead of X whenever they have scientific tests that show Y. Lastly, you could show that this is the only test that has ever shown Y, and every other test completed by independent researchers gets Z.

Alternatively, if the expert is not basing their conclusion on a specific scientific test but on their generalized experience, research, or knowledge in the field, you should attack that as a weakness as well. On cross-examination, exploit the expert’s inability to articulate a concrete basis for their conclusions. The key to this line of questioning is to force the expert to drill down on specifics, and demonstrate that the expert cannot cite the studies or provide enough information on the science to warrant their reliance on it.

For example, if the opposing expert refers to a study, ask for detailed specifics including when, where, and how the study was conducted. Ask things that you know the opposing expert does not know. The more you induce the expert to say “I don’t know,” the more you underscore that their opinion is groundless, and founded on something they don’t actually know very well. Once you’ve concluded this line of questioning, it can be exceedingly effective to close by asking if the opposing expert can provide anything else to support their opinion. When they, predictably, say “no,” you’ll have substantially eroded the strength of their testimony.

In sum, foundational attacks when cross examining an expert witness requires forcing the expert to be as specific as possible in articulating the basis for their opinion. Don’t allow them to rely on what they know from experience or give vague, broad answers. Only when the expert witness identifies specific facts, studies, and sources to support their opinion can you effectively undermine their conclusion and their impact on the case.