Perfecting Expert Testimony at PTAB

Expert testimony plays a critical role in Patent Trial and Appeal Board (PTAB) proceedings at the U.S. Patent and Trademark Office (USPTO). Thousands of petitions for inter partes review (IPR) and post grant review have been filed with PTAB since these filings were allowed in 2012.

In PTAB’s America Invents Act (AIA) proceedings, a private party may file a petition asking a panel of three administrative patent judges (APJs) to review a previously issued U.S. patent to determine whether it fails to satisfy certain conditions of patentability and should be canceled. The panel initially issues a decision reflecting its determination whether to institute a full trial. If so, the case proceeds to a final written decision, entered after an opportunity for briefing, evidence and oral argument (if requested) from both parties. That final written decision may be appealed to the U.S. Court of Appeals for the Federal Circuit, but the panel’s initial decision whether to institute trial may not be appealed. See, e.g., 35 U.S.C. §§ 311–319.

Expert testimony is presented in almost all cases, for good reason. It helps PTAB understand the technology at issue and, more importantly, it gives insight into how that technology would have been understood by a person of ordinary skill in the art (POSITA) — the hypothetical person having ordinary skill and knowledge in the relevant technology, from whose perspective certain questions of patentability are assessed. This can be instrumental when PTAB evaluates the patentability of challenged claims.

As a PTAB APJ for nearly 10 years, I experienced firsthand the value that well-presented expert testimony can provide to the panel. However, certain predictable pitfalls continue to permeate parties’ use of expert witnesses, damaging their expert’s credibility and diminishing the weight given to their testimony. Common pitfalls include a lack of support for the expert’s testimony, improper incorporation by reference, improper gap filling and failure to satisfy the qualifications of a POSITA. Such pitfalls can be avoided with diligent and skillful preparation.

Basis for Expert Testimony at PTAB

The Federal Rules of Evidence (FRE) generally apply to PTAB proceedings. FRE 702 explains that a “witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise” if the expert’s knowledge (a) “will help the trier of fact to understand the evidence or to determine a fact in issue,” and the testimony (b) “is based on sufficient facts or data,” (c) “is the product of reliable principles and methods,” and (d) “the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.”

Expert testimony may be offered for many purposes. PTAB’s Consolidated Trial Practice Guide (CTPG) provides the following nonlimiting examples of circumstances where expert testimony may assist PTAB to:

• explain the relevant technology;
• establish the level of skill in the art and describe the POSITA;
• explain the teachings of the prior art and how they relate to the patent’s claims;
• address whether a POSITA would have found a reason to modify the prior art and, if so, whether there would have been a reasonable expectation of success;
• explain how evidence of objective indicia of non-obviousness should be weighed against evidence of unpatentability; and
• explain the nature and import of such objective indicia.

Additionally, expert testimony may be relied upon to support a party’s proposed construction of critical claim language or to support arguments regarding public accessibility.

Introduction of Expert Testimony at PTAB

At PTAB, all evidence — including expert testimony — must be filed as an exhibit in the proceeding. Expert testimony may be offered as direct testimony, in the form of a declaration or affidavit, or as cross-examination testimony, in the form of a deposition transcript. Live testimony is rarely permitted at PTAB and is not an expected mechanism to introduce expert opinion evidence.

A party may submit expert testimony with their substantive papers. A petitioner typically will offer direct testimony through an expert declaration accompanying its petition. Such a declaration may support the petitioner’s asserted grounds of unpatentability, for example, to explain the basis on which a POSITA would have understood that the asserted prior art discloses each limitation of the challenged claims.

A patent owner may submit expert testimony with its pre-institution preliminary response. Regardless of whether a pre-institution expert testimony is filed, a patent owner typically will offer its expert’s direct testimony as a competing declaration accompanying its response and may introduce pertinent cross-examination testimony of the petitioner’s expert. A patent owner’s declaration may identify weaknesses in the petitioner’s grounds, for example, by opining that a POSITA would not have understood that a particular claim limitation is disclosed by the prior art.

After the initial papers are filed, some limitations exist. Namely, the petitioner may not submit evidence, including expert testimony, that could have been presented earlier in the proceeding, for example, evidence directed to the petitioner’s prima facie unpatentability case. That evidence must accompany the petition. A petitioner may, however, submit new expert testimony with its reply, to rebut arguments made in the patent owner response. In its sur-reply, the patent owner may only submit pertinent cross-examination testimony of any reply witnesses put forth by the petitioner.

PTAB’s Weighing of Expert Testimony

PTAB has broad discretion to evaluate witness credibility and to determine the weight it will give to expert testimony. PTAB APJs are statutorily required to possess “competent … scientific ability” and, therefore, they examine the quality of expert testimony against that background of scientific understanding.

However, to be given weight, PTAB regulations reinforce that expert testimony must be based on sufficient facts and data. Specifically, 37 C.F.R. § 42.65(a) states that “[e]xpert testimony that does not disclose the underlying facts or data on which the opinion is based is entitled to little or no weight.” Accordingly, it is essential that any expert testimony offered to PTAB makes clear the facts and data that form the basis of the expert’s opinion, lest it be disregarded outright.

Common Pitfalls in Offering Expert Testimony

1. Conclusory and Unsupported Testimony

PTAB’s rules are clear: PTABwill give “little or no weight” to expert testimony that is insufficiently supported. Despite this explicit regulatory caution, and despite former USPTO Director Kathi Vidal’s 2023 designation of a precedential decision reinforcing this point, parties continue to submit expert testimony that does not sufficiently explain the bases for the expert’s conclusions, leading PTAB to discredit the witness and discount, or disregard entirely, their testimony. See, e.g., In re American Academy of Science Tech Center, 367 F.3d 1359, 1368 (Fed. Cir. 2004) (“[T]he [PTAB] is entitled to weigh the declarations and conclude that the lack of factual corroboration warrants discounting the opinions expressed in the declarations.”).

This issue can arise at institution and may push the needle in favor or against institution of trial. For example, PTAB recently denied institution in TikTok Inc. v. NTech Properties, Inc., IPR2024-01339, Paper 9 (PTAB Feb. 25, 2025) where the petitioner’s contentions regarding the prior art were insufficiently explained and supported. The PTAB gave “little or no weight” to the testimony of the petitioner’s expert because the declaration was wholly “conclusory” — “repeat[ing], almost verbatim, the language in the Petition without any further explanation or supporting reasoning or evidence.”

Expert testimony offered by patent owners may suffer the same deficiency, as demonstrated in Arashi Vision (U.S.) LLC (d/b/a Insta360) v. GoPro, Inc., IPR2024-01165, Paper 11 (PTAB Jan. 22, 2025). In its preliminary response, the patent owner offered an expert declaration to support its argument that two pieces of prior art were “technically incompatible” such that a POSITA would not have combined them. PTAB declined to credit the expert’s testimony, however, because the expert did not provide “sufficient technical reasoning explaining how using the buffer for one purpose precludes its use for another purpose. Patent Owner cites its declarant … but his testimony merely repeats Patent Owner’s arguments without any meaningful elucidation. On this record, we are shown no technical impediment with using the buffer … as proposed in the Petition.” Accordingly, PTAB instituted trial.

To be sure, this issue arises post-institution as well and may be dispositive to the panel’s choice to credit one party’s expert over the other. For example, in reaching its final written decision in Sony Interactive Entertainment LLC v. Quantum Imaging, LLC, IPR2023-00095, Paper 53 (PTAB Dec. 9, 2024), the panel weighed the testimony of the parties’ competing experts. The panel determined that aspects of the petitioner’s expert testimony was “entirely without support either in [the prior art reference] or from any persuasive supporting reference or evidence that it was known, at the time of filing of the application which became the [challenged] patent.” The panel noted that the testimony was not supported by any “textbook, technical disclosure, or other independent evidence.” Accordingly, PTAB credited the testimony of the patent owner’s expert witness and determined that the petitioner failed to meet its burden to demonstrate the unpatentability of the challenged claims on that ground.

In other words, PTAB will not take the expert’s word for it. To avoid such a fate, practitioners must ensure that the expert testimony upon which they rely adequately cites sufficient underlying evidence, facts, data and/or technical reasoning to support the testimony. This can be done through the expert’s citation to, and discussion of, additional corroborating evidence, e.g., patents, textbooks, articles, or other publications, that support or explain the expert’s conclusions and are offered as appendices or exhibits to the declaration.

2. Improper Incorporation by Reference

PTAB practitioners must thread an important needle — sufficiently articulating and supporting their arguments, including with expert testimony, while also complying with PTAB’s word count limitations. PTAB’s rules are clear that this cannot be achieved by incorporating arguments and evidence from an expert declaration into the party’s paper. “Arguments must not be incorporated by reference from one document into another document.” 37 C.F.R. § 42.6(a)(3).

PTAB’s prohibition against incorporation by reference in part seeks to honor the word limits set forth in 37 C.F.R. § 42.24(a). Presenting material in an expert declaration and incorporating it in a party’s brief by reference circumvents the applicable limits and gives the offending party an unfair advantage. As stated in the CTPG, “[t]he rules governing the conduct of AIA trial proceedings were designed to promote fairness and efficiency…. [P]arties that incorporate expert testimony by reference in their petitions, motions, or replies without providing explanation of such testimony risk having the testimony not considered by the Board.” CTPG 35-36. Furthermore, incorporation by reference complicates the record and risks confusion in identifying which arguments a party properly made, and to which opposing counsel may have an opportunity to respond.

The Federal Circuit agrees. For example, in 3M Company v. Evergreen Adhesives, Inc., 860 Fed. Appx. 724 (Fed. Cir. 2021), the court affirmed PTAB’s decision that certain arguments were improperly incorporated by reference through the expert’s declaration where “3M’s filings never sufficiently made the relevant ‘contention’ or argument at all, and instead supported 3M’s position entirely by reference to [its expert’s] declarations and testimony.”

It is important to balance these completing tensions: minding PTAB’s word limit while also providing sufficient argument and supporting evidence in the paper itself. This is where prioritization and efficient drafting pays dividends. While it may be tempting to present multiple asserted grounds and/or arguments, that should not be done at the expense of a sufficient presentation in the party’s brief, with expert testimony offered for additional support and elaboration but without improper incorporation by reference.

3. Improper Gap-Filling

Expert testimony is helpful in establishing how a POSITA would have viewed the prior art and is relevant to alleged anticipation or obviousness of the challenged claims. However, petitioners proceed at their peril when relying on expert testimony to fill in gaps or to supply limitations that are missing in a prior art reference.

Regarding anticipation, the CTPG explains that “a petitioner asserting anticipation cannot rely on its expert to supply disclosure of a claim element that is not expressly or inherently present in the reference.” CTPG 36. It is improper, for example, for a petitioner asserting anticipation to rely on expert testimony that the provision of such a limitation would involve only common sense or ordinary skill. See, e.g., Scripps Clinic & Rsch. Found. v. Genentech, Inc., 927 F.2d 1565, 1576 (Fed. Cir. 1991) (“The role of extrinsic evidence is to educate the decision-maker to what the reference meant to persons of ordinary skill in the field of the invention, not to fill gaps in the reference. If it is necessary to reach beyond the boundaries of a single reference to provide missing disclosure of the claimed invention, the proper ground is not § 102 anticipation, but § 103 obviousness.”).

Regarding obviousness, the CTPG also explains that “in an obviousness analysis, conclusory assertions from a third party about general knowledge in the art cannot, without supporting evidence of record, supply a limitation that is not evidently and indisputably within the common knowledge of those skilled in the art.” CTPG 36; see also above (regarding conclusory and unsupported testimony).

Therefore, it is important that expert testimony is relied upon to shed light on the import of prior art disclosures themselves and is not relied upon to supply claim limitations that are missing in the prior art. “In other words, expert testimony may explain ‘patents and printed publications,’ but is not a substitute for disclosure in a prior art reference itself.” CTPG 36.

4. Lacking Status as a Person of Ordinary Skill in the Art

PTAB’s CTPG was last revised in 2019 and is outdated in certain respects. For example, the CTPG states that “[t]here is … no requirement of a perfect match between the expert’s experience and the relevant field. A person may not need to be a person of ordinary skill in the art in order to testify as an expert under Rule 702, but rather must be ‘qualified in the pertinent art.’” CTPG 34 (quotations and citations omitted).

The unwary practitioner following this guidance, however, may encounter trouble. In 2022, after the last CTPG revision, the Federal Circuit stated the contrary:

Kyocera Senco Ind. Tools, Inc. v. Int’l Trade Comm’n, 22 F.4th 1369, 1376-77 (Fed. Cir. 2022).

It is essential, therefore, that practitioners ensure that their expert witness meets the appropriate qualifications of a POSITA in the pertinent art and, if known and different, the qualifications likely to be proposed by the opposing party. Where an expert witness fails to qualify as a POSITA, PTAB has afforded no weight to their testimony concerning issues that turn on the perspective of a POSITA. See, e.g., Avail Medsystems, Inc. v. Teladoc Health, Inc., IPR2022-00444, Paper 10 at 24-27 (PTAB July 21, 2022) (“[T]he definition of a skilled artisan we have adopted for this Decision, which was proposed by Petitioner and Dr. Stone, requires at least two years of research or work experience in designing or engineering teleconferencing systems, such as those used in telemedicine. Although Dr. Stone has advanced degrees in electrical engineering and extensive experience with medical devices, he lacks specific experience researching or engineering teleconferencing systems, such as those used in telemedicine…. Therefore, it would be inappropriate for us to consider any testimony by Dr. Stone on any issue that is analyzed through the lens of an ordinarily skilled artisan.”).

It is important to note, however, that PTAB may be willing to splice portions of the expert’s testimony and consider those portions for which expertise is not disputed and qualification as a POSITA is not required. For example, in Avail Medsystems, the panel concluded that “[a]lthough we do not give any weight to Dr. Stone’s testimony from the perspective of a skilled artisan, we find him qualified to opine about the technology itself that is the subject matter of the [challenged] patent and the asserted prior art. In other words, we may consider Dr. Stone’s opinions about the structures and operations included in the disclosed systems, but we cannot give any weight to his opinions regarding what a skilled artisan would have understood and/or derived from the disclosed technology because the latter is necessarily from the perspective of a skilled artisan.” Notwithstanding the panel’s willingness to dissect the expert testimony in that case, careful attention to the proposed qualifications of a POSITA may have avoided this outcome.

Conclusion

Expert testimony is an important part of practice before PTAB. When care is taken to avoid these common pitfalls, expert testimony can help support a party’s case in ways helpful to PTAB. Failure to recognize these pitfalls, however, risks a costly endeavor in futility if PTAB determines that the expert’s testimony should be afforded no weight.