4 Keys To A Successful Daubert Challenge

It's critical to understand what a successful Daubert challenge looks like in order to point out the opposing expert's weaknesses.

Anjelica Cappellino, J.D.

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— Updated on September 27, 2021

4 Keys To A Successful Daubert Challenge

Since the United States Supreme Court decided a standard for the admissibility of expert testimony in the seminal case, Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), an increasing number of expert witnesses have been challenged by way of a Daubert motion. In cases that hinge on expert testimony, a Daubert motion can threaten all parties. As such, experts should be retained, prepared, and scrutinized with vigor. If you are the challenging party, however, it is critical to understand the foundation for a successful Daubert challenge so that you can effectively exploit the opposing expert’s weaknesses.

Aside from enumerating the factors that determine whether an expert’s testimony is admissible, Daubert notably stressed the importance of the trial judge’s gatekeeping function in excluding unreliable and irrelevant expert testimony. As a result, appellate courts oftentimes affirm the admissibility determinations of the trial judge—even more of a reason to succeed with your Daubert challenge the first time around. Below are some tips on successfully challenging the opposing side’s expert.

1) Focus on the Daubert Factors

 This should go without saying, but the individual factors enumerated in Daubert should always be considered when drafting any successful motion to exclude expert testimony. Daubert was decided in response to the older standard, established in Frye v. United States, 293 F. 1013 (D.C. Cir. 1923), which held that an expert’s testimony must be based on a technique that is “generally accepted” in the scientific community. The decision in Daubert, however, effectively overrode general acceptance as the central criteria for admissibility, instead, focusing on a non-exhaustive list of factors which include:

  1. Whether the expert’s technique or theory can be or has been tested—that is, whether the expert’s theory can be challenged in some objective sense, or whether it is instead simply a subjective, conclusory approach that cannot reasonably be assessed for reliability
  2. Whether the technique or theory has been subject to peer review and publication
  3. The known or potential rate of error of the technique or theory when applied and the existence and maintenance of standards and controls
  4. Whether the technique or theory has been generally accepted in the scientific community

Currently, all federal courts and approximately 27 states have adopted the Daubert standard. While Daubert still maintains general acceptance as a considered factor, the decision highlights the importance of other considerations, particularly reliability. When critiquing the opposing side’s expert in a Daubert jurisdiction, the expert opinion must be analyzed from all angles. It is not simply enough that the expert may fail on one factor, as the other factors might favor admissibility. On the other hand, because the factors are not bright line rules, one particularly strong factor (for example,  utilizing a tried-and-true testing approach) can outweigh the weaknesses in other aspects of the technique.

2) Critique the Methodology

While not one Daubert factor is dispositive, one word is consistently at the forefront of most successful Daubert challenges: methodology. The importance of methodology is evinced in the Court’s consistent holdings, both in Daubert and its progeny, that the reliability of the expert’s methods, opposed to the conclusions, should be the focal point of the analysis. As codified in Rule 702 of the Federal Rules of Evidence, an expert’s opinion must be based on sufficient facts or data that is the product of reliable principles and methods reliably applied to the facts of the case.

While the stark contrast of an opposing expert’s conclusions can seem glaring, attacking the conclusion itself does not help when challenging admissibility. Rather, a Daubert motion should analyze how the expert reached its conclusions, what methodology was used, and what was lacking in that approach to result in an opinion contradictory your own. Of course, the specific weaknesses of an expert’s opinion can vary widely, but generally speaking, there are certain things that should be analyzed. What testing did the expert employ? What is the rate of error? Were any controls in place? Was the data properly interpreted? Breaking down the expert’s technique and pointing out its weaknesses will naturally expose that their conclusion is incorrect.

3) Assess Potential Conflicts of Interest

An expert can sometimes be excluded from testifying for reasons not directly related to their opinions. If a conflict of interest exists that renders the expert too biased to give a reliable opinion, the trial court has discretion to exclude the expert’s testimony and disqualify them as a witness. Conflicts of interest issues usually arise in circumstances wherein an expert was formerly employed by, or previously hired as, an expert for the opposing party. If you are challenging the opposing expert on these grounds, you must establish, by a preponderance of the evidence, that

  1. It was reasonable to conclude that a confidential relationship existed between yourself and the expert prior to the opposing party’s retainer
  2. Confidential or privileged information was disclosed to the expert

While the disqualification of expert witnesses on these grounds are not common, it may be worth investigating the opposing expert’s past affiliations, particularly in small, niche practice areas in which the likelihood of a past relationship with your client is heightened.

Daubert was decided over two decades ago, which means there exists a plethora of case law and rulings to research. Unless you are arguing before a new judge, chances are most trial judges have previously ruled on Daubert motions. Use the judge’s record to your advantage to ascertain important information such as the judge’s interpretations and general leanings when it relates to expert testimony. By educating yourself on the judge’s record, you can craft your motion to reflect the considerations that your particular judge cites when determining expert admissibility.

On a more general level, keep in mind the overall judicial opinion of the expertise in which your witness works. Not all experts are created equal, as some sciences are more lauded and accepted than others. For example, courts do not overwhelmingly admit psychology experts, with one study showing that testimony of psychologists was admitted only 49.7% of the time. On the other hand, there are certain experts that are consistently allowed to testify, such as law enforcement experts, which are shown to be admitted about 85.7% of the time.

Overall, by analyzing the trial court’s previous rulings, controlling case law, and the general acceptance of the type of testimony you seek to exclude, you can successfully challenge the opposing side’s expert and in turn, potentially change the outcome of the case.

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