What to Include in an Expert Rebuttal Report

What is a Rebuttal Report?

A rebuttal report analyzes and refutes the positions the opposing expert takes in their expert witness report. A good rebuttal report will establish a foundation for questioning the expert’s credibility. Through this foundation developed and the analysis presented, the strongest rebuttal reports also demonstrate that the rebutting author took the best route available for understanding the issues in the case.

When a rebuttal report does double duty in this way, it not only exposes weaknesses in the opposing expert’s conclusions but also reaffirms the strength of the conclusions reached by the rebuttal’s writer in their own expert witness report.

Steps For Critiquing The Opposing Expert

A well-crafted rebuttal report requires a strategic approach to dissect and critique the opposing expert's analysis. These steps provide a foundation for a persuasive and legally sound response.

1. Consider the Scope of the Rebuttal

In the context of rebuttal experts, Rule 26(a)(2)(D) of the Federal Rules of Civil Procedure allows the evidence to be admitted if it “is intended solely to contradict or rebut evidence on the same subject matter,” and must be disclosed 30 days after the other party’s disclosure. A “rebuttal expert report is not the proper place for presenting new arguments unless presenting those arguments is substantially justified and causes no prejudice.” Courts have wide discretion in the admissibility of expert evidence and can strike a rebuttal expert’s disclosure if it goes beyond its permissible scope. For example, if the report “fails to provide scientific disagreement” with the opposing expert’s construction, or it contains “substantial new data and information” exceeding the original report.

Although an expert’s rebuttal report should not contain new opinions or information that contradicts the initial report, it need not be stricken if it is “an elaboration of and [is] consistent with an opinion/issue previously addressed” in the expert’s initial report. A report “may cite new evidence and data so long as the new evidence and data is offered to directly contradict or rebut the opposing party’s expert.” In other words, there is no “bright line rule” that every expert opinion “must be included in a preliminary report, or forever be precluded.” That being said, it is important to be mindful of the content of the rebuttal report so that it does not go beyond its permissible scope.

2. Learn the Opposing Expert’s Opinion

Any strong rebuttal thoroughly understands the arguments, methods, and conclusions presented by the opposing party. Start by reading the report to get familiar with its layout, contents, and conclusions. Then, reread it, focusing on areas of weakness within the methods, analysis, and conclusions. Many expert witnesses perform this step with a pen or highlighter handy so that they can make notes for themselves.

Before challenging the opposing expert’s opinion, it’s essential to understand the basis of that opinion and the foundation on which it was formed. A critical analysis ensures that any challenge to the opinion is meaningful and precise, rather than a broad dismissal. Take time to identify specific aspects of the opposing expert’s argument that are either incorrect or contradictory to your side’s position.

While reading critically, it is helpful to note any areas where the opposing expert’s report aligns with the findings or positions presented in the initial expert report. Recognizing areas of agreement not only narrows the focus of the rebuttal to key points of contention but also demonstrates an unbiased approach by acknowledging similarities rather than solely opposing the opposing expert’s conclusions.

Like any strong rebuttal, opposing arguments need to be fully understood before they can be effectively challenged. A thoughtful rebuttal should demonstrate not only a grasp of the opposing arguments but also a balanced and systematic critique that highlights the strengths and weaknesses of each point.

3. Recreate the Opposing Expert's Analysis

Once a clear understanding of the opposing expert’s assumptions, methods, analysis, and conclusions has been established, it may help to attempt to recreate the opposing expert’s analysis. Such a recreation can reveal specific flaws in the expert’s approach. It can also reveal how that flawed approach led to flawed conclusions.

Not all cases will lend themselves to a recreation of an opposing expert’s analysis. Time and resources may be scarce, for example, or the opposing expert’s approach may depend on factors that can’t easily be recreated. In these cases, an expert may nevertheless benefit from walking through each step of the analysis, imagining how it would have been carried out in practice, and looking for flaws.

During this process, stay alert both for explicit assumptions and implicit assumptions. Explicit assumptions are typically stated outright—they’re known to the opposing expert and may be factored in as part of the conclusion. Implicit assumptions, however, may not be stated outright. in fact, the opposing expert may not even be aware of them but they nevertheless affect the conclusion.

Addressing both explicit and implicit assumptions can help an expert write a clearer rebuttal, especially if any assumption affects the conclusions reached.

4. Challenge the Methodology

Identify any clear, objective errors, such as errors of fact or mistakes in calculation. Such errors do not appear in every expert witness report. But when they do, they provide a clear, easily-evaluated starting point for discussing weaknesses in the report.

Focus on any contradictions within the report. Contradictions and inconsistencies often indicate flaws in methodology, analysis, or resulting conclusions. Examples include inconsistent use of inputs, switching methodologies, or citing and quoting sources selectively or out of context.

As aptly stated in the seminal United States Supreme Court decision, Daubert v. Merrell Dow Pharmaceuticals, Inc., there are several factors that should be considered by a court when determining the admissibility of expert testimony. While no one factor is deemed more important than another, it would be remiss to ignore the significance of the first listed factor: whether the expert’s technique or theory can be or has been tested. That is, whether the expert’s theory can be challenged in some objective sense, or whether it is instead simply a subjective, conclusory approach that cannot reasonably be assessed for reliability.

The takeaway point of this factor is that admissibility rests on methodology as opposed to conclusions. In other words, an expert’s opinion should derive from a reliable, objective methodology. In accordance with this factor, the methodology of an opposing expert’s opinion should be critiqued first. The ways in which a specific methodology can be challenged are as numerous as the fields of expertise themselves.

• Does your rebuttal agree with the type of testing conducted?
• If the type of testing was correct, is the potential rate of error accurate?
• Do peer review and the opposing expert’s reputation in the scientific community factor in?
• Were inconsistent testing or analysis methodologies utilized?

By focusing on the weaknesses or inconsistencies in the opposing expert’s methodologies, a rebuttal report becomes substantially more persuasive.

5. Provide Alternatives

As you identify issues, provide alternatives where possible. For example, if a mathematical equation was solved incorrectly, provide the correct solution, and explain how the correct solution affects the opposing expert’s conclusions. If the opposing expert quotes a source out of context, provide the context and explain its effects on the expert’s report and the case as a whole.

As held in Deseret Management Corp. v. U.S., a “rebuttal expert may introduce new methods of analysis in a rebuttal report as long as the new method is offered to contradict or rebut an opposing party’s expert.” In Deseret, for example, a rebuttal report applied a different valuation method in estimating the value of a license at issue. The court found that the report was properly submitted, even though it applied, a “new, alternative theory,” because both reports addressed the same subject matter and the rebuttal report was offered to contradict the opposing party’s report. Therefore, rebuttal reports need not avoid alternatives or new means of testing if they are offered to contradict the opposing side’s arguments.

Finally, it's essential to avoid contradictions between the initial report and the rebuttal report. Ideally, the rebuttal should reinforce the accuracy of the original work, supporting its findings as well-founded and credible.

Rebuttal reports require experts to balance multiple perspectives at once. They also require experts to think critically about their own and an opposing position simultaneously. This exercise in critical thinking, done well, can have a profound effect on a client’s case.