Clarifying the “Obvious Alternative Causes” Standard in Expert Testimony under Rule 702

Introduction

In Faison-Williams v. United States, 24-1404 (2d Cir. Apr. 1, 2025), the Second Circuit addressed for the first time how rigorously a district court must evaluate an expert’s handling of alternative explanations under Federal Rule of Evidence 702. Natasha Faison-Williams sued the United States under the Federal Tort Claims Act (FTCA), alleging that her Veterans Affairs surgeon negligently scheduled and supervised a thoracic microdiscectomy. The district court excluded her causation expert for “failing to rule out obvious alternative causes” and granted summary judgment for the government. On appeal, the Second Circuit vacated and remanded, holding that the district court erred in setting too high a bar and misapplying the “obvious alternative causes” inquiry.

Parties:

Plaintiff-Appellant: Natasha Faison-Williams
Defendant-Appellee: United States of America

Key Issues:

Did the plaintiff exhaust FTCA administrative remedies?
Did the district court abuse its discretion in excluding expert testimony under Rule 702 for failure to address obvious alternative causes?

Summary of the Judgment

The Second Circuit unanimously held:

The administrative claim, though brief, sufficiently alerted the Veterans Affairs to challenge the decision to schedule the thoracic surgery, satisfying the FTCA’s presentment requirement.
The district court abused its gatekeeping discretion under Rule 702 by requiring the expert to “rule out” every alternative cause rather than assessing whether he had “adequately accounted for obvious alternative explanations.”
Because renomination of the expert’s testimony may create genuine issues of material fact on causation, the summary judgment must be vacated and the case remanded for further proceedings.

Analysis

1. Precedents Cited

McNeil v. United States, 508 U.S. 106 (1993) – FTCA exhaustion requirement.
Johnson v. United States, 788 F.2d 845 (2d Cir. 1986) – Sufficiency of administrative claim for FTCA presentment.
Collins v. United States, 996 F.3d 102 (2d Cir. 2021) – Requirements for specificity in § 2675(a) presentment.
Daubert v. Merrell Dow Pharm., 509 U.S. 579 (1993) – Reliability and relevance as gatekeeper standards for expert testimony.
Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999) – Applying Daubert to non-scientific expert testimony.
Amorgianos v. Nat’l R.R. Passenger Corp., 303 F.3d 256 (2d Cir. 2002) – Abuse‐of‐discretion review of Rule 702 exclusions.
Fed. R. Evid. 702 Advisory Committee Notes (2000 Amendment) – “Obvious alternative explanations” as a relevant reliability factor.

2. Legal Reasoning

The Court’s reasoning unfolds in two parts:

Jurisdiction and Presentment: By presenting a one-page VA claim alleging that the surgeon “deviated from the accepted standard of medical care,” Faison-Williams gave the agency enough specificity to investigate both surgical performance and the decision to operate. Under Johnson and Collins, a claimant need not plead every detail so long as the agency can value and settle the claim.
Rule 702 Gatekeeping: District courts must assess whether an expert’s methodology is reliable and whether it helps the jury. Among the factors is whether the expert has “adequately accounted for obvious alternative explanations.” The district court here demanded that the expert “rule out” every competing cause—cervical myelopathy, preexisting bladder issues, childbirth trauma, psychological overlay—an overly stringent standard. The appellate court emphasized that an expert need only non-conclusorily explain why alternative explanations are less persuasive, based on experience, imaging, studies, and accepted medical literature.

3. Impact

This decision will guide courts in future Daubert analyses by clarifying:

Lower courts should not elevate “obvious alternative causes” into a categorical requirement that each cause be conclusively ruled out.
Experts must provide reasoned, experience-based explanations distinguishing their causation theory from plausible alternatives.
Gatekeepers retain discretion to exclude testimony that lacks any engagement with alternatives, but must respect expert methodologies that handle them adequately.

In medical malpractice and other complex torts, this ruling reduces the risk that otherwise reliable experts will be excluded for failing to achieve complete certainty on competing hypotheses.

Complex Concepts Simplified

Federal Tort Claims Act (FTCA): A statute allowing suits against the U.S. government for torts by federal employees, but only after the claimant first files an administrative claim (“presentment”).
Daubert Standard (Rule 702): Federal rule requiring judges to act as gatekeepers, ensuring expert testimony is both reliable (methodology sound) and relevant (helps jury).
“Obvious Alternative Explanations” Factor: A question in the reliability inquiry: does the expert acknowledge and explain why common competing causes are unlikely? It is not an absolute requirement to eliminate all other possibilities.
Conversion Disorder / Psychological Overlay: A condition in which a patient’s symptoms appear neurological but have a psychological origin. Experts must distinguish this from structural injuries by correlating symptoms with imaging and objective tests.

Conclusion

Faison-Williams v. United States refines the Court’s gatekeeping role under Rule 702. It confirms that district courts must measure an expert’s engagement with alternative causes with realistic rigor, not an impossibly high bar. By vacating the exclusion of the causation testimony, the Second Circuit preserves plaintiffs’ ability to present expert evidence where methodologies are sound and alternatives are reasonably addressed. This decision thus reinforces both Daubert’s flexibility and the jury’s role in resolving genuine factual disputes.