Evan M. Tager is a partner with Mayer Brown LLP in the firm’s Washington, DC office and is the WLF Legal Pulse’s Featured Expert Contributor on Judicial Gatekeeping of Expert Evidence. Geoffrey M. Pipoly  is a senior associate in the firm’s Chicago, IL office.

As practitioners who work with expert witnesses know well, Federal Rule of Evidence 702 and Daubert v. Merrell Dow Pharmaceuticals1 require district judges to perform, before trial, a “gatekeeping role” to determine whether proposed expert testimony “rests on a reliable foundation and is relevant to the task at hand.2  Sometimes, however, district courts fail to conduct their gatekeeping role rigorously, and admit into evidence at trial shaky or unreliable expert opinions on the theory that the opinions’ deficiencies bear on the weight—and not the admissibility—of the opinions.  A recent decision from the Fourth Circuit, Sardis v. Overhead Door Corporation,3 reaffirmed the critical importance of the gatekeeping function under Daubert, and sent a strong message to district courts to stop punting that function to juries. 

The defendant in Sardis manufactured garage doors, the metal hoods the garage doors are installed in, and the packaging used to ship those products.  In 2014, the defendant redesigned the handholds on the packaging container that was used to hold the garage doors and hoods for shipping.  An employee of one of the defendant’s independent distributors grabbed one of the handholds of a container that was perched on a forklift, the handhold gave way, the container fell on him, and he died from his injuries.  His estate sued the defendant, alleging design defect, negligence, breach of warranty, and failure to warn.4

“[T]he only probative evidence supporting [the plaintiff’s] claims came from two expert witnesses”5: Drs. Singh and Wogalter. Dr. Singh was a packaging engineer who opined that the defendant’s new packaging was deficient under relevant industry standards.  He also opined that the deficiencies proximately caused the decedent’s death.  Dr. Wogalter was an expert on “human factors,” which is a “discipline of study that deals with the design of products and systems based on peoples’ abilities and limitations to promote productivity, satisfaction, and safety.”  Dr. Wogalter opined that the defendant should have done field testing on the new handholds, that the lack of warnings on the handholds made them unreasonably dangerous, and that these failures proximately caused the decedent’s death.6 

Before trial, the defendant filed motions to exclude both experts, but the district court denied the motions, “making no relevancy determinations” and ruling that vigorous cross-examination and appropriate jury instructions could resolve any deficiencies in the experts’ methods.  The case went to trial, the experts testified consistent with their pre-trial written reports, and the jury returned a more than $4 million verdict for the plaintiff.   After trial, the defendant filed a motion for judgment as a matter of law under Rule 50(b), renewing its Daubert challenges.  The district court denied that motion, and the defendant appealed.7

The Fourth Circuit reversed the jury verdict, reasoning that the district court abused its discretion when it ruled that “the issues of relevance and reliability impacted only the weight of the experts’ testimony, not their admissibility.”  The Fourth Circuit explained that the district court’s “error was harmful for two independent reasons.  First, without Drs. Singh’s and Wogalter’s testimony, [the plaintiff] could not have prevailed on any of its claims as a matter of law.  And second, assuming that the court had considered the merits of [the defendant’s] Daubert challenges in ruling on [the defendant’s] post-trial Rule 50(b) motion, it abused its discretion in refusing to strike Drs. Singh’s and Wogalter’s testimony for both offered irrelevant and unreliable opinions.”8

The Fourth Circuit first addressed the district court’s ruling on the defendant’s pre-trial Daubert motions.  The Fourth Circuit reasoned that the district court’s ruling “dismissed each of [the defendant’s] reliability and relevance arguments as only going to weight, not admissibility.”  By doing so, the Fourth Circuit, explained, the district court “abandoned” the gatekeeping role that Daubert requires district courts to perform.9 

Next, the Fourth Circuit flatly rejected the district court’s rationale for denying the defendant’s post-trial motion for judgment as a matter of law—that, because the jury found Drs. Singh and Wogalter’s testimony credible despite vigorous cross-examination, no harm was done.  The Fourth Circuit held that the district court had “improperly delegated its gatekeeping responsibility to the jury,”10 explaining:

[C]redibility is entirely distinct from reliability and relevancy, which are preconditions to the admissibility of expert testimony.  While cross-examination may be a proper tool to determine which of two competing experts’ theories more credibly explains an event, even a thorough and extensive examination does not ensure the reliability or relevance of an expert’s testimony.11

The Fourth Circuit emphasized that its ““insistence on district courts’ compliance with Rule 702’s plain gatekeeping requirement stems not from an arbitrary adherence to procedural formality” but from the fact that “‘expert evidence can be both powerful and quite misleading.’”12  Therefore, “the importance of the gatekeeping function cannot be overstated.”13

The Fourth Circuit also explained that its ruling was “confirmed by the Advisory Committee on Evidence Rules’ current proposal to amend Rule 702,” which had been unanimously approved by the Committee in April 2021.  As the court indicated, the advisory committee notes explain:  “‘[U]nfortunately many courts have held that the critical questions of the sufficiency of an expert’s basis [for his testimony], and the application of the expert’s methodology, are generally questions of weight and not admissibility.  These rulings are an incorrect application of Rules 702 and 104(a) and are rejected by this amendment.’”14

The Fourth Circuit went on to address the merits of the defendant’s Daubert challenges. 

The Fourth Circuit observed that although the defendant’s packaging was made of wood, Dr. Singh relied on an industry standard applicable to cardboard packaging “as the relevant benchmark, and the district court erroneously permitted him to do so before the jury.”15  The court explained that a “design standard that does not even apply to the product at issue categorically lacks a valid scientific connection to the pertinent inquiry.  It is, in simpler words, the touchstone of irrelevancy under Daubert.”16

The Fourth Circuit also criticized the district court for admitting Dr. Singh’s causation opinion even though he “conducted no testing whatsoever to arrive at his opinion,” made no effort “to create a computer generated or physical model of the container,” and in fact rejected the defendant’s offer to construct three exemplars of the container.17  Thus, the Fourth Circuit concluded, Dr. Singh’s causation opinion rested on nothing more than his own ipse dixit, which is impermissible under Daubert.18  

The Fourth Circuit made quick work of Dr. Wogalter’s opinions.  The court explained that Dr. Wogalter’s opinion about whether the defendant should have known that its packaging container was dangerous was “incompatible with the governing Virginia” state-law “‘reason to know’ standard.”19  It was thus irrelevant.  The Fourth Circuit also declared the opinion unreliable, explaining that because Dr. Wogalter “utilized no specified methodology . . . his theories could not have been subjected to peer review.  In fact, he conceded that there is no existing literature on how to test human factors that he knows of.”20  The Fourth Circuit went on:

Nor could Dr. Wogalter describe any other prior case in which he, or any other expert, conducted a hazard analysis on a similar container that also involved an allegedly defective handhold.  Nowhere in his testimony did he offer any facts, test data, or peer-reviewed literature for reaching his conclusion.  Thus, it was impossible for the district court, and impossible for us on appeal, to ascertain the potential rate of error in Dr. Wogalter’s hazard analysis approach and whether hazard analyses are widely accepted in the field of “human factors.”21

Sardis should serve as a reminder to judges and practitioners alike that Daubert’s gatekeeping requirement is not a mere suggestion, but a threshold requirement of every federal case that involves expert testimony. 


  1. 509 U.S. 579 (1993).
  2. Id. at 597.
  3. 10 F.4th 268 (4th Cir. 2021).
  4. Id. at 275-77.
  5. Id. at 275.
  6. Id. at 277-78.
  7. Id. at 278-79.
  8. Id. at 281.
  9. Id. at 282 (cleaned up).
  10. Id. at 283 (cleaned up).
  11. Id. at 282 (citation omitted).
  12. Id. at 283 (quoting Daubert, 509 U.S. at 595).
  13. Id. (cleaned up).
  14. Id. at 284 (emphasis added).
  15. Id. at 288.
  16. Id. (cleaned up).
  17. Id. at 291.
  18. Id. at 292.
  19. Id. at 294.
  20. Id. at 295. (cleaned up).
  21. Id. at 295-96.