Helpful tips about expert witnesses in patent cases (no matter where the IP dispute is tried)

12 minute read
26 July 2021

Last month, Gowling WLG's intellectual property professionals hosted an on-demand webinar that discussed how you can prove and protect ownerships of your IP through expert evidence. Here are the key takeaways from the panel.

Types of IP cases

In patent cases, expert witnesses are almost always called upon to render expert opinions concerning claim construction and the issues of infringement and invalidity.

In some trademark cases a survey expert is utilized to prove the likelihood of confusion.

In some copyright music cases an expert might be needed to analyze an aspect of the accused musical score, such as chord progression, to determine infringement.

In IP cases dealing with damages, it is common to utilize an expert who is very experienced in quantifying damages and regularly testifies on such matters.

Finding an expert

To find a technical expert witness in a patent case it is advisable to start with the client's engineers or scientists with expertise in the relevant technology and product to identify individuals in both industry and academia with the right qualifications and experience. It is also worthwhile looking at research expert lists and organizations, bios of university professors and information about experts who have testified in similar or relevant cases. Another approach is to contact experienced lawyers to obtain names of experts they would recommend.

Once a list of potential experts is developed, then it is important to do research on each expert concerning prior testimony, publications, and public statements, looking for any prior positions that would be detrimental to the opinions needed in the present case.

From this effort, a short list is developed. Each expert on that list is then interviewed to determine their opinions, technical qualifications, abilities to teach and explain, and how well they would testify, especially on cross examination.

An experienced expert would tend to be easier to work with, and present well, although a professional expert can sometimes be seen as a gun for hire. That is someone who no longer practices in the area of expertise, but rather spends most or all of their time testifying in court. That type of expert begins to look more like a partisan advocate than an independent expert. This is especially true (i) if expert always acts for the same client or type of client, or (ii) if it can be shown that the expert's opinion on the same subject matter has changed over time, seemingly to suit the client's needs.

What to expect from your expert

Expert witnesses must be independent and remain objective. Their duty is to the Court, not to the party who is paying them.

An expert witness is not an advocate for the party. They have a special duty to the court to provide fair, objective and non-partisan assistance on matters relating to their expertise.

Expert witness reports are mandatory across all jurisdictions. It is important to have the expert draft the report after discussions with the lawyer about the issues to be addressed and the opinions that will be needed for trial. When the draft is completed, the expert and the lawyer should then discuss the draft, with the lawyer making both stylistic and substantive suggestions to make sure the report is relevant and readable. The final report will be influenced, and to some extent guided, by the lawyer. However, the lawyer must never change the opinions of the expert or the basis for those opinions. The use of diagrams, charts, videos, and analogies can help with explaining both the opinions and the basis.

Special considerations across the jurisdictions

United States

In the United States, the vast majority of intellectual property cases are tried to a jury. As a result, expert witnesses are a necessity to address those issues that are beyond the common experience and understanding of lay jurors.

In the United States, there are no formal or statutory rules concerning how an expert is retained and instructed. Each attorney will instruct the expert on the issues to be addressed and the opinions needed according to their individual styles and practices.

In the U.S., virtually all communications between and attorney and the expert witness can be discovered by the other side. Also, it is important for the expert to testify that he or she wrote the expert report to assure the jury that the expert is independent and not just a mouthpiece for the lawyers. At times, to avoid this issue, the attorneys will agree not to examine the expert about the level of attorney participation in drafting the report.

In the U.S., the courts do not get involved with the expert witness until shortly before trial, usually at the time dispositive motions are filed. Any challenges to expert witnesses are made in the form of what we call "Daubert motions." By law, the court is charged with being a gatekeeper to prevent unreliable expert testimony from reaching the jury. The court must determine through a Daubert motion whether the expert's testimony is:

  1. based on sufficient facts and data
  2. a product of reliable principles and methods
  3. a product of reliably applying those principles and methods to the facts and data

The court must determine, in the words of the U.S. Supreme Court, whether the expert's opinion "represents a valid scientific connection to the pertinent inquiry."


Federal Court's Code of Conduct for Witnesses provides:

An expert witness named to provide a report for use as evidence, or to testify in a proceeding, has an overriding duty to assist the Court impartially on matters relevant to his or her area of expertise.

This duty overrides any duty to a party to the proceeding, including the person retaining the expert witness.

Instructing experts is not as formalized as in the UK – there are no specific rules or methodology that prescribe the process. Nevertheless, a proposed expert witness who is unable or unwilling to comply with the code of conduct, or is not qualified to give expert opinion evidence, will not be permitted to do so.

But some important points to note:

  1. the opinion must be that of the expert's
  2. communications with expert are producible
  3. drafts of reports are not always producible, but in some circumstances can be
  4. instructions are usually set out in the retainer letter, and repeated/revised in the final report.

For these reasons, normally would speak with the expert several times, before asking the expert to reduce report in writing and provide you with a draft.

At times, it is advisable to have two separate experts:

  1. one to advise and assist you in preparing for discoveries/depositions
  2. one to prepare report and testify.

In some provincial Superior Courts, judges will order experts to 'hot tub'. Courts have used it as a pre-trial procedure in which experts meet without counsel present. Experts try to narrow issues by indicating areas in which they agree and produce a report. Hot tubbing orders are not often made in pure IP cases.

When expert is first presented at trial, they have to be "tendered" and accepted as expert. It is similar to the Daubert process in the US, except it is not by way of but rather the expert is put on stand, and explains their qualifications/expertise and independence, and then their evidence is "tendered" to the court by counsel asking the court to accept the expert in specified area of expertise. The opposing party can cross-examine to undermine the purported expertise/qualifications. The judge then has to accept or reject expert and define the parameters of the testimony that will be permitted.


In preliminary injunction proceedings the petitioner and / or respondent will bring their own (written) expert evidence particularly when it will be difficult to decide about an infringement or obviousness.

In nullity proceedings, it is unusual to have expert witnesses because the judges at the Federal Patent Court are engineers / scientists.

It is absolutely necessary for experts to testify in motions for inspection of an item or a process pursuant to section 140c of the Patent Act (the German equivalent of "pretrial discovery"). The patentee has to demonstrate "sufficient likelihood" of an infringement – that can normally only been done by means of an expert opinion.

In trademark cases, an expert from an empirical legal research institute will try to demonstrate by taking a survey that the mark has acquired a "reputation" (Art. 9 para 2 c EUTM Regulation) and is "well known".


The term "expert witness" is not explicitly stipulated in China's legal system. However, there are two types of litigation participants in civil proceedings who take on a similar role as the expert witnesses: the first one is the supporting expert instructed by the parties and sometimes by the court, and the other one is the court's internal technical investigator.

For example, a party may apply for a person with expertise to appear in court and give an opinion on the authentication reports or professional issues. This "person with expertise" is similar to but differs from an expert witness in the common law system, because his or her opinion is not a witness testimony and cannot be considered as evidence, but rather as a statement of the parties themselves. As such a person with expertise only serves as a technical assistant to the parties and is therefore referred to as the supporting expert in China.

On the other hand, in China, although some specialized IP courts across the country have been established and have centralised jurisdiction over technical cases, unlike technical judges in Germany, the majority of IP Judges in China are law judges without strong science and engineering background. As such, the mechanism of technical investigator was devised in 2015 by the SPC. The value of the technical investigator lies in assisting judges in making technical determinations.


There are detailed Civil Procedure Rules, Guidance Notes and Court Judgments that prescribe how expert witnesses are to be independent and objective.

It is vital, as a lawyer, that the manner and content of all of your communications with your expert from investigation to retention to proof of evidence to preparation for trial is in line with the case law, guidance notes and rules of procedure. Otherwise, the evidence will be tainted and accorded little weight by the Court.

Get in touch

Our international network of IP professionals is here to help you navigate the latest developments in IP around the globe. If you have any questions or need assistance, get in touch with any member of our team.

For more on expert evidence, check out our latest on-demand webinar from our Lifecycle of Smart Idea series where our panel of IP professionals cover a wide array of topics from search to retention to experts for interim applications.

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