Daubert at the PTAB vs. District Court: Two Different Worlds

A patent expert who clears Daubert in the Eastern District of Texas is not the same expert in front of the Patent Trial and Appeal Board. The same declaration, the same CV, the same methodology can survive in one forum and fail in the other, because the two forums use different rules to decide what testimony counts.

District courts apply Federal Rule of Evidence 702. The PTAB does not. That single fact drives most of the doctrinal divergence below, and it has real consequences for how parties draft expert declarations and how they plan parallel proceedings.

How district court gates expert testimony

Federal Rule of Evidence 702, as amended effective December 1, 2023, requires the proponent of expert testimony to establish, by a preponderance of the evidence, that the witness is qualified, that the testimony is based on sufficient facts or data, that it is the product of reliable principles and methods, and that the expert has reliably applied those principles and methods to the facts. The 2023 amendment did not change the underlying Daubert framework. It clarified that the four reliability requirements are admissibility questions for the court, not weight questions for the jury.

The mechanism is exclusion. A district court that finds an expert opinion unreliable strikes it. The jury never hears it. Partial exclusions are more common than full exclusions, and the partial-to-full ratio in patent cases sits at roughly 2 to 1 in the post-amendment period, but the operative remedy is the same: the testimony is removed from the case.

Federal Circuit decisions have reinforced this gatekeeping function. EcoFactor v. Google (Fed. Cir. 2025) (en banc) vacated a damages award where the expert's royalty-rate analysis was not adequately tied to the underlying license agreements, and the court framed the problem as a Rule 702 reliability failure. More recent Federal Circuit damages decisions have reinforced this gatekeeping function on apportionment grounds.

How the PTAB weighs expert testimony

The PTAB applies Rule 702 only loosely. The Board sits as a tribunal of administrative patent judges, not as an Article III court with a jury, and its rules of evidence are governed by 37 CFR 42.62, which incorporates the Federal Rules of Evidence with narrow carve-outs for criminal and jury provisions. There is no front-end Daubert motion. There is no admissibility hearing. As a practical matter, the Board does not exclude expert testimony; it weighs it.

Practitioners sometimes file motions to exclude under 37 CFR 42.64, but those motions are limited to admissibility grounds like relevance and hearsay; reliability arguments are treated as going to weight. The standard treatment is that reliability arguments go to the weight the Board gives the testimony, not its admissibility. The Board may credit an expert in full, credit the expert in part, or decline to credit the expert. The final written decision states which, and the credit determination is reviewed on appeal under the substantial-evidence standard.

The Federal Circuit has accepted this division. The Board's credibility findings are entitled to deference on appeal, and the court has repeatedly declined to import Rule 702's gatekeeping mechanics into the PTAB context. Commentary from Patents Post-Grant and other post-grant practice groups has tracked this distinction since the early days of inter partes review, and the underlying rule has not shifted.

The practical effect is that an expert whose methodology would draw a Daubert challenge in district court can still testify at the PTAB. The Board reads the declaration, listens to the deposition, and decides how much weight to give it. There is no procedural off-ramp.

Where the divergence matters

The divergence becomes operational when a patent is in parallel litigation. A district court case and an IPR proceeding can run on the same patent at the same time, with different parties, different counsel, and sometimes overlapping experts. The same expert declaration, filed in both forums, will be tested under different standards.

In district court, opposing counsel will file a Daubert motion. The court will rule before trial. If the motion succeeds, the testimony is out. If it fails, the testimony goes to the jury, with cross-examination as the limiting mechanism.

In the IPR, the petitioner or patent owner will challenge the same expert in briefing. The Board will weigh the testimony in the final written decision, often spending paragraphs explaining why it credits or discounts particular conclusions. If the expert's methodology is weak, the Board will say so in the FWD, and that adverse credibility finding is now part of the expert's public record.

This creates a feedback loop that retaining counsel should track. An adverse credibility finding in an FWD does not bind a district court, but it is a fact the district court can consider. Opposing counsel will cite it in the next case. The expert's PTAB credit-rate history becomes evidence in subsequent retention decisions.

Implications for declaration drafting

A declaration drafted for one forum is not automatically usable in the other. For district court filings, the declaration should anticipate Rule 702 challenge. Every methodological step should be tied to a reliability anchor: the technical literature, the file history, the comparable licenses, the prior testimony. The expert's qualifications should map cleanly to the technology, with the POSITA framing front-loaded.

For PTAB filings, the declaration is read by judges who will weigh it, not exclude it. The premium is on internal consistency and on explicit reasoning. The Board credits experts who walk through claim-by-claim analysis with citations to the underlying art. It discounts experts who recite conclusions without showing the connecting steps. Boilerplate hurts. Specificity helps.

When the same expert is used in parallel proceedings, the cleanest approach is to draft once for the more rigorous forum, which is district court, and then file a parallel declaration at the PTAB that does not contradict the district court version. Contradictions between the two declarations are the easiest cross-examination material an opposing expert can ask for, and the PTAB will note them in the FWD.

A note on the data

The aggregate outcome patterns referenced above draw on patent expert declarations, PTAB final written decisions, and district court Daubert rulings tracked on WitnessLens since 2010. The post-amendment Daubert outcome split (roughly 51 percent admitted, 35 percent partial exclusion, 14 percent full exclusion) and the partial-to-full ratio are calculated from merits rulings on patent expert testimony on WitnessLens. Methodology details are on the methodology page.