The Testimony Types Expert Witnesses Need to Know

For professionals looking to expand into expert consultation, it’s important to be aware of the different roles and expert types involved in legal proceedings.

Carolyn Casey, J.D.

Written by
— Updated on May 20, 2022

The Testimony Types Expert Witnesses Need to Know

An expert’s role can be thought of as a sports broadcaster covering a basketball season. They’re on the sidelines commenting on strategy and helping the audience understand key moments of a live game. They can also offer a more analytical look at a game by offering player or team statistics. Often, they’ll be asked to weigh in on the technical aspects of a controversial foul during the broadcast or on a post-game show where the hosts may challenge their assumptions. And of course, they write blogs and articles to report on season-long game outcomes.

Much like a broadcaster, expert witnesses can be called upon for assistance or opinions at various stages of a case. Where they’re needed will depend on the case itself and the attorney’s argument. But their primary goal is to aid understanding of crucial case facts and defend their expert opinions if challenged by the opposition. Here, we’ll explore the multitude of ways experts may be called upon to aid case comprehension and offer professional analysis within a legal proceeding.

Expert Witness Report

As a lawyer evaluates a case, they may seek an expert to help them understand complicated or technical facts. In medical cases, for example, lawyers frequently ask medical experts to review case records and information to help them determine what the medical standard of care is for the situation. From here, an expert can help guide their understanding of whether a party failed to live up to that standard of care, and if that failure resulted in injuries to the claimant. The medical expert will review the records, conduct independent research if needed, and present their findings in a written report.

This written report—and expert witness report— is a key document that informs both defendant and plaintiff lawyers as they gauge the merits of a case and consider their strategies for either defending or proving certain claims. Expert witness reports are also used to prepare for interviews with other key individuals related to the case or even for deposition. Experts who have contributed reports may also be asked to testify at trial and present their conclusions. In these cases, federal and some state rules mandate that attorneys disclose that the expert will be a witness and also provide the expert report to the opposition. However, if the report is considered privileged information containing legal strategies, it may be withheld.


Part of the legal process involves interviewing the opposition’s witnesses ahead of a trial in order to prepare their case and cross examination questioning. Known as a deposition, the opposing counsel asks an expert witness a series of questions relating to the facts of the case, and perhaps to the expert’s credentials. Statements, opinions, and facts recorded in depositions are also commonly used to try to convince the opposing party that a settlement is the best outcome. Depositions can be lengthy, stressful events.

Whatever an expert says in the deposition can also be brought up at trial during cross examination to undermine the expert’s testimony or credibility. The deposition becomes a record and can be entered as evidence and used to impeach an expert. We’ve all seen those dramatic television courtroom scenes where a lawyer challenges an expert’s statement with a quoted claim they made earlier. This scenario underscores the need for the expert to be consistent in what they say in depositions and later in any courtroom testimony.

As an expert, it’s key to study your report findings and answer consistently with those findings at a deposition. Keep the facts of the case at hand and give accurate, consistent, and objective answers to ensure deposition success.

Direct Testimony

As a case progresses and the parties are unable to reach a reasonable settlement agreement via deposition, you may be asked to testify in court. Your job in this context is to help the jury understand facts that are too technical or complex for a layperson to understand. Your client will ask you questions in the courtroom to help the jury comprehend the relevant case issues. You may also be asked to give opinions on certain aspects of the case or likely outcomes of actions.

The lawyer will also ask you questions designed to establish your qualifications as an expert witness.  This is where you will state your educational credentials, certifications, specialties, and relevant professional experience. This is an important stage as it conveys to the jurors why they should listen to and believe your testimony. You must be perceived as an expert in the subject matter at hand and function as a neutral educator. For the jury, you’re there to help them decipher and understand technical facts they must consider as the triers-of-facts in legal cases.

Cross Examination

After your direct testimony, the opposition has the opportunity for cross examination—a follow-up interrogation of your initial testimony. Be aware that opposing counsel’s goal is to convince the jury to disregard everything in your testimony that helps the other side. They will try to catch you in contradictions or inconsistencies in your in testimony as compared to your deposition. A common tactic is also to try to get you to opine on something helpful to their case or for you to speculate. Here, you simply answer the questions as best you can, and politely decline to answer any questions that require you to speculate or give an opinion outside the scope of your expertise.

As an expert, if your credibility or statements are attacked during cross examination, your client can still provide evidence to support you. Typically, they will ask you to take the stand again and ask you questions to re-establish your credibility or establish that your testimony was not inconsistent with prior statements as painted during cross examination.

Rebuttal Testimony

After the defense presents its case, at the discretion of the judge, a plaintiff may be allowed to use rebuttal witnesses. Rebuttal expert witnesses, for example, are brought in to help the prosecution demonstrate that a defendant’s arguments are erroneous or false. Once the rebuttal evidence is presented, the defense can cross examine the rebuttal expert. Though not used very often, defense counsel can also ask the judge to permit them a “surrebuttal” to show the rebuttal evidence was false.

There are special rules governing rebuttal evidence. For example, rebuttal evidence is only admissible when the plaintiff could not have foreseen the need for it when they presented their case-in-chief. (Plaintiff’s present their case first in legal proceedings.) The rebuttal evidence must be confined to the subject matter of the evidence being rebutted, and not used merely to bolster the plaintiff’s case.

The Wide Scope of Expert Witness Usage

There is quite a wide variety of uses for expert witnesses in legal proceedings.  Just like a sports commentator opines in different settings and stages of a game or season, experts may appear throughout the case lifecycle and bring specialized knowledge and clarity to the case at hand. Whatever situation you find yourself in as an expert in the legal arena, remember your role is always to be a neutral, objective expert helping the jury understand facts related to your area of expertise. With this knowledge, you’ll be able to perform comfortably in any legal expert role, at any case stage.

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