Navigating the Standards of Admissibility for Expert Testimony

In the courtroom, rules of evidence aren’t just technicalities—they’re game changers. Among them, one rule stands out. It decides whether expert witnesses can share their specialized knowledge. This single decision can directly affect the outcome of a case.

Rule 702

• Helpfulness: The expert’s scientific, technical, or specialized knowledge will help the trier of fact understand the evidence or determine a fact in issue.
• Sufficient Basis: The testimony is based on sufficient facts or data.
• Reliable Principles and Methods: The testimony is the product of reliable principles and methods.
• Reliable Application: The expert has reliably applied those principles and methods to the facts of the case. (This was emphasized in the 2023 amendment to prevent “overstatement” by experts.) [law.cornell.edu], [arnoldporter.com].

The Daubert Standard

The United States Supreme Court addressed how expert testimony should be handled in Daubert v. Merrell Dow Pharmaceuticals, Inc. In that case, the Court provided five key factors to consider when determining whether expert testimony is admissible under Federal Rule of Evidence 702:

• Testability: Whether the theory or technique can be empirically verified through testing.
• Peer Review and Publication: Whether the theory or technique has been subjected to peer review and publication supporting acceptance within the scientific community.
• Known or Potential Error Rate: Identifying the error rate to ensure reliability and consistency.
• Existence and Maintenance of Standards: Whether there are standards controlling the technique’s operation as well as clear protocols reducing subjectivity.
• General Acceptance: Whether the theory or technique is generally accepted within the scientific community.

These five factors are not rigid; they are flexible guidelines to help judges act as “gatekeepers” ensuring that expert testimony is relevant and reliable.

Klein v. Meta

Once case which highlights the importance of Rule 702 is Klein v. Meta. In that case Facebook users filed suit against Meta. The plaintiffs argued that Meta created a monopoly on personal social networking services by misrepresenting data collection and privacy practices. They claimed that in a competitive market, Facebook would’ve paid users for access to their data.

The plaintiffs brought in an expert to certify a nationwide class of Facebook users, Dr. Nicholas Economides, who concluded that Facebook users would’ve been paid $5 per month for access to their data. However, the court found that his conclusion wasn’t backed by any evidence or support. Importantly, the court did not challenge the truth of the claim itself, but rather the methodology used to reach it. It therefore denied class certification in a major setback for the plaintiffs.

Since both eminent domain matters and property tax appeal cases almost always involve expert witnesses, the admissibilty of expert testimony is at the forefront of importance in these types of matters.

New Jersey Transit Corp. v. Franco

An eminent domain case that highlights the importance of expert testimony is NJ Transit Corp v. Franco. That case involved a dispute over a 1.89-acre property spanning Hoboken, Union City, and Weehawken. NJ Transit condemned the property for public use, initially offering $934,500. A jury later awarded $8.15 million based on its “highest and best use” for residential development. NJ Transit appealed the verdict, and the case found its way to the Appellate Division.

One of the issues on appeal involved the property’s highest and best use, specifically whether a cul-de-sac could be constructed to access planned high-rise and mid-rise apartments. If the defendants could demonstrate a reasonable probability of obtaining a use variance or acceptance as a public street, then the cul-de-sac would’ve supported a higher valuation for the property. The defendants relied on expert testimony that Weehawken had no discretion to approve the variance and that approval wasn’t needed in the first place. While the trial court admitted these opinions, the Appellate Division found that such testimony was legally inadequate and prejudicial. First, approval was indeed required through either a use variance or accepting the cul-de-sac as a public street. Second, the experts failed to show a reasonable probability of obtaining such approvals. This was necessary to support the highest and best use valuation. As a result, the Appellate Division reversed the trial court’s $8.15 million verdict and remanded for a new trial on just compensation.

Conclusion

Rule 702 and the Daubert standard are cornerstones for expert testimony. Courts apply high standards and will strike expert testimony if it fails to meet those standards. As the above two cases demonstrate, this can have serious repercussions for litigants. Those who intend to rely on expert testimony in court should ensure that it checks all the boxes for admissibility.  Where the witness or witnesses face challenges as to the admissibility of their expert opinions, it is common for the court involved to conduct a “gatekeeping” hearing, sometimes referred to as a Rule 104 hearing, before the court, in order for the court to determine whether expert testimony, in whole or in part, is admissible before the case is presented to the jury or other trier of fact.  Parties involved in these specialized types of litigation, and their proposed expert witnesses, need to anticipate that a Rule 104 hearing may occur and need to be prepared!