United States: Planning Your First (or Fiftieth) Expert Challenge From Depositions Through Trial

A motion to exclude expert testimony can be a powerful tool to encourage settlement, win summary judgment, or challenge class certification. The primary goal of such a motion is, obviously, to prevent the introduction of expert evidence at trial. But these motions can also have the added purposes of both educating the court on the science underlying the case, as well as demonstrating to the other side your willingness and readiness to defend against their claims. That said, you should not file such a motion without first carefully considering the applicable legal standard, the testimony and expert you plan to challenge, and your overall likelihood of success.  

Ascertain the proper standard.

The first step in preparing to challenge an opposing expert is figuring out the applicable standard. Federal courts and most (~75%) states adhere to the Daubert standard, while a minority of states (including my home state of Pennsylvania) use the Frye standard, and there are even a few states which have a hybrid of the two. If you don't already know the standard applicable in your jurisdiction, you can quickly figure it out via a brief search on Westlaw, Lexis, or even Google.

The Frye standard is based on an old case out of the D.C. Federal Court of Appeals: Frye v. United States, 293 F. 1013 (D.C. Cir. 1923). Under Frye, the test for admissibility of expert testimony is based upon the "general acceptance" of the expert's methodology in the relevant scientific community. Proponents of the Frye test argue that it appropriately places the evaluation of a methodology's value in the hands of scientists, and not the courts; however, the Frye test also necessarily makes it harder for newer methodologies and techniques—no matter how valuable or valid—to find their way into a courtroom.

The Daubert standard, which is applied by most jurisdictions, evolved from Frye and is based on the 1993 case Daubert vs. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). The Daubert test officially made the court the "gatekeeper" tasked with determining itself whether the expert testimony to be offered is relevant and reliable. The Daubert decision established a series of factors to assist the court in so determining—e.g., whether a theory or technique has been tested; whether it was subjected to peer review and publication; the potential rate of error; and the "general acceptance" of the theory (the prior Frye test). Subsequent cases added additional factors and made it clear that the Daubert test applies to all expert testimony, not just testimony of a scientific nature.

In addition to the above common-law tests, be sure to check the applicable rules of evidence. For example, Federal Rule of Evidence 702 codified the Daubert standard, stating that a qualified expert's testimony may be permitted if "(a) the expert's scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; and (d) the expert has reliably applied the principles and methods to the facts of the case."

Finally, in addition to the above standards regarding experts, don't forget the fall-back of Federal Rule of Evidence 403 (or its state equivalent)—namely, that the testimony to be offered should be excluded when it is more prejudicial and confusing than probative.

Preparing your challenge.

Once you've nailed down the appropriate standard, the first thing you must do is determine your objective: What do you hope to achieve with your motion? Do you want to completely disqualify the expert? Or do you just want to partially eliminate or otherwise limit his or her testimony?

Obviously, your objective will necessarily depend upon what you think you can achieve and what weaknesses you identify. Work with your own expert to identify flaws in the opposing expert's methodology or qualifications to ascertain what it is you will attack.

Will you challenge the expert's qualifications? See if the expert is offering opinions beyond her area of expertise. Examine her degrees and professional association memberships. Are her organizations substantive? Or do some of them merely require that one write a check to join? Some experts may even create organizations or associations to fluff their CVs. Do some digging.

Will you challenge the expert's methodology? Perhaps the expert has relied on insufficient or unreliable data. Maybe her methodology is too subjective, or was not peer-reviewed. If the methodology itself is sound, does it fit the facts of the case? Does the expert adequately explain how the methodology can apply to the legal question at issue? If the expert has a separate professional practice, are there inconsistencies between the expert's methodology and that practice?

Much of your preparation will involve learning the underlying science. Ask your own expert questions, and read the relevant literature. Get a technical dictionary applicable to the field, and refer to it frequently. Be patient, as you are outside your area of expertise and must take the time to learn.

If the expert has testified before, track down her prior testimony if possible so that you can highlight any inconsistencies. If your jurisdiction allows it, prepare for and take the expert's deposition (more on this below) for use at the hearing and/or at trial.

Examining the expert at a deposition or Frye/Daubert hearing.

As laid out above, if your jurisdiction permits it, you will likely want to depose the opposing expert. But even if you cannot, you may have to cross-examine the expert at the Frye/Daubert hearing itself. When doing so, remember: you are not at trial. Focus on the expert's methodology and qualifications, not on bias or other thematic issues you want to save for the jury.

At the hearing, you can highlight prior inconsistent testimony, point out flaws in the expert's testing, and even give the expert a "test" on the relevant science (e.g., to define a term, identify the position of various professional organizations on the subject, etc.) to highlight a lack of knowledge—though this latter tactic can sometimes backfire with experienced experts. If you can, use demonstratives, even a simple graph or bulleted list of points. These can greatly aid the judge, who may be completely unfamiliar with the underlying science.

When should you make the motion?

As a general rule, you should make the motion as early as you can. Your goal is to knock out some testimony and get a settlement or summary judgment. Some courts have explicitly held that such motions to exclude must be made prior to trial, but even if your jurisdiction has no such rule, it is wise practice. If you wait until trial, opposing counsel may sneak some previews of the questionable testimony into an opening, which could taint the jury. At that point, the judge might be more willing to allow the testimony to go forward, and a motion to strike after the fact is of very limited use if the jury has already heard the information.

Make sure to follow local practice and rules regarding deadlines and the form of the motion as well. For example, courts may require multiple orders (e.g., one setting a briefing schedule and hearing, and one actually granting the motion), affidavits of a competing expert, etc. The last thing you want is to have your motion thwarted by a procedural oversight.  

Even if you have grounds for a motion, you may not want to file one.

A Frye/Daubert motion can be a useful tool to promote a quick resolution to a case, but a failed motion has its own risks: Your motion and cross-examination has given the expert a preview of your examination at trial. She can correct her testimony, fill in the holes, and think up answers to your more difficult questions. Keep in mind that some studies (e.g., a 2010 study by PwC) have revealed that motions to exclude experts succeed less than half the time. If your motion is not particularly compelling, you may want to forgo it completely and reserve your best arguments for trial.  

What if you motion fails?

If your motion fails, you will have to face the expert at trial. This could be the subject of an entirely different article, but there are a few basic tips based on the above.

First, make a plan. Figure out your objectives in advance. Generally, at trial, you will not be trying to show that the expert is technically wrong because the jury may not understand an overly technical cross, and even if you win such an argument on some arcane scientific point, they may not notice. If you lost your motion, remember: if the judge did not believe that the expert's science was actually wrong, the jury may not either.  

Accordingly, you may want to shift from a technical attack to a more persuasive presentation. Get the expert to concede facts or elements he can't deny that are important to your case. If there are any easily assailable items in his method, focus only on those. Highlight inconsistencies in his prior testimony. Bring up the fact that he is being paid. Your primary goal should be to give the jury reservations about the expert that you can exploit in your closing.

Some notes of caution: If an expert has previously testified in many cases, you may be tempted to paint him as a "career" witness, but this is not always wise, as some juries may positively view such experience as indicative of expertise. (As in, "Wow! This guy must be smart! People want him to testify all the time!") Do not let the expert lead you off course on a tangent (unless you know where it is going), and if this happens inadvertently, always bring the examination back to your plan and question. Also, be wary of attacking the expert on technical grounds as it can confuse the jury, and, if you're not successful, end up strengthening the expert's position.

Finally, if you lost an earlier challenge to the expert, make sure to preserve your right to appeal by making an objection when the testimony is offered at trial or at any other appropriate time in accordance with the applicable rules.


Motions to exclude expert testimony, when done properly, remain a very effective way to obtain an early resolution to a claim. Although the above tips are certainly not an exhaustive guide to such motions, it is my hope that they are useful to you in filing, arguing, and (hopefully) winning your next expert challenge.  

Originally published in by DRI's, Trials and Tribulations newsletter

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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