Understanding the Different Standards Between IPRs and District Court Litigation

When challenging the validity of a U.S. patent, litigants face a choice between district court litigation and the Patent Trial and Appeal Board (PTAB) through an Inter Partes Review (IPR). While both forums assess the same core question—whether a patent claim is valid—the standards applied differ significantly, and those differences can shape litigation strategy.

1. Burden of Proof

• District Court (Litigation):

  
  

  A patent is presumed valid under 35 U.S.C. § 282. Therefore, the challenger must prove invalidity by “clear and convincing evidence”, a high evidentiary burden that favors the patent owner.

• IPR (PTAB):

  
  

  The petitioner must establish unpatentability by a “preponderance of the evidence”—meaning “more likely than not.” This is a lower burden than in litigation, making it easier to invalidate claims in an IPR. 

  
  

2. Claim Construction Standard

• District Court:

  
  

  Claims are construed under the Phillips standard, which interprets claim terms according to their ordinary and customary meaning as understood by a person of ordinary skill in the art at the time of invention. Courts consider the specification, prosecution history, and extrinsic evidence.

• IPR (PTAB):

  
  

  Since November 2018, the PTAB also applies the Phillips standard (previously, it applied the broader “broadest reasonable interpretation” standard). This change brought greater consistency between PTAB and district courts, though differences can still arise in application.

  
  

3. Admissibility of Evidence

• District Court:

  
  

  Courts allow a wide range of evidence, including live expert testimony, depositions, fact discovery, and cross-examination at trial. Juries may also be involved, adding unpredictability.

• IPR (PTAB):

  
  

  Evidence is generally limited to patents and printed publications, expert declarations, and affidavits. There is no live testimony (except in rare circumstances at oral hearings), and discovery is narrower, often limited to what is necessary “in the interests of justice.”

  
  

4. Decision-Makers

• District Court:

  
  

  Cases may be decided by judges or juries. Juries are often sympathetic to patent owners and may not fully grasp technical complexities, which can work to the patentee’s advantage.

• IPR (PTAB):

  
  

  Decisions are made by administrative patent judges (APJs) who are specialists in patent law and technology. This can cut both ways: APJs are less likely to be swayed by emotion, but they are also more skeptical of broad claims.

  
  

5. Speed and Cost

• District Court:

  
  

  Patent litigation can last several years and cost millions of dollars in attorney fees, expert reports, and discovery.

• IPR (PTAB):

  
  

  IPRs are faster and cheaper—statutorily designed to conclude within 12–18 months of institution, with costs typically ranging from several hundred thousand dollars to around one million.

  
  

6. Estoppel Effects

• District Court:

  
  

  Losing on invalidity defenses in litigation does not prevent a party from raising similar arguments in other cases (subject to issue preclusion and claim preclusion rules).

• IPR (PTAB):

  
  

  Estoppel is stronger. A petitioner who receives a final written decision is barred from raising in district court or the ITC any ground of invalidity that was raised or reasonably could have been raised in the IPR.

  
  

Strategic Takeaways

• Patent Owners often prefer litigation due to the higher burden of proof, jury involvement, and broader evidentiary record.

• Accused Infringers often favor IPRs for their lower burden, specialized judges, and speed.

• In practice, many defendants pursue a dual-track strategy, filing IPRs while defending litigation, hoping the PTAB will invalidate key claims and shift settlement leverage.

  
  

Comparison of Standards: IPR vs. District Court Litigation

Category	IPR (PTAB)	District Court Litigation
Burden of Proof	Preponderance of the evidence (“more likely than not”)	Clear and convincing evidence (high evidentiary standard)
Claim Construction	Phillips standard (ordinary/customary meaning to POSITA)	Phillips standard (same framework, but may be applied differently by courts)
Evidence Allowed	Primarily patents and printed publications; expert declarations; limited discovery	Wide evidentiary record, including live expert testimony, depositions, documents, and fact witnesses
Decision-Makers	Administrative Patent Judges (APJs) – technically trained, patent specialists	Judges or juries – generalists; juries may be sympathetic to patent owners
Timeline	12–18 months to final decision (statutory deadline)	Often several years before trial and appeal
Cost	Hundreds of thousands to ~$1M (generally lower cost)	Several million dollars (much higher litigation expense)
Estoppel	Bars petitioner from raising in litigation any ground that was or could have been raised in the IPR	Losing in court does not bar raising new grounds in future cases (subject to preclusion rules)
Strategic Impact	Faster, narrower, more technical review; favored by accused infringers with close prior art	Broader evidentiary and procedural protections; higher burden favors patent owners

Conclusion

While both IPRs and litigation test patent validity, the different standards of proof, claim construction, and decision-making processes mean that the choice of forum can dramatically impact outcomes. For patent owners, recent PTAB guidance (such as stricter enforcement of claim element mapping) may help restore balance, but IPRs remain a formidable tool for challengers.