Expert Witness

The term “expert witness” is used to describe a person who is called upon to testify during a trial due to his knowledge or skills in a field that is relevant to the case. For example, an expert witness may be a blood spatter analyst who can testify as to the type of weapon that was used to commit a murder. Using this information, the defense can then prove the defendant did not commit the crime he is being accused of. To explore this concept, consider the following expert witness definition.

Definition of Expert Witness


  1. A person who provides testimony during a trial due to his particular knowledge or skills in a field that relates to the issues that are being discussed in the case.


1325 – 75         Middle English (expertus)

Expert Witness Fees

When an expert witness is called to testify for a case, there are expert witness fees that must be paid. After all, the expert is being called away from his work to provide testimony, and as such he should be paid for his time. Most expert witnesses require a retainer up front, just like lawyers do. An average retainer for an expert witness is about $2,000, but the total may add up to much more, depending on the expertise and experience of the expert.

On average, expert witnesses who mostly testify on behalf of defendants charge more than those who more often testify on behalf of plaintiffs. Also, those who are brought in to testify for plaintiffs are more likely to charge an up-front retainer.

Lawyers may sometimes try to save a few dollars on expert witness fees by not hiring such a professional, and it is true that many cases do not necessitate this expenditure. However, this is not a time to pinch pennies. For example, an expert witness can make or break a case. Often the most expensive witnesses are the most effective. Lawyers often find they get what they pay for if they try to hire a less expensive expert witness.

Expert Witness Testimony

Expert witness testimony can truly change the outcome of certain cases. Experts can offer information that can help strengthen the case for either the prosecution or the defense, depending on the kind of experts they are. However, just because an expert provides testimony, that doesn’t automatically guarantee a positive outcome for the side that called the witness. Some experts may provide testimony that seems weak, or otherwise like they would say anything just for a paycheck.

The main point of expert witness testimony is for the expert to teach the jury about a difficult topic of which he has superior knowledge. This means that the expert must break down all of the jargon and industry speak so that it is easier for the jury – and everyone else – to understand. The expert must be able to communicate in a way that is not so technical. Miscommunication has been many an expert witness’ downfall because it is sometimes difficult to explain a concept that they otherwise know so well.

Some experts get carried away and say much more than they need to in order to answer the question posed to them. This can end up hurting the case, rather than helping it. It can also confuse the jury if the expert continues to ramble on with no clear explanations behind what he is saying.

Types of Expert Witness

There are a number of types of expert witnesses that can be called upon in a case, all of which can be grouped into five major categories: medical, financial, forensic, vocational, and mental health.

Medical Expert

Medical expert witnesses are perhaps among the most common types of expert witness. This is because they can testify in cases ranging from car accidents to medical malpractice, and even violent crime. Usually medical experts are doctors, but they can also be specialists in a particular field. Medical Examiners (MEs) are often called upon to testify about the factors that may have contributed to a person’s death.

Financial Expert

Financial experts are often brought in for cases involving some sort of finance-related crime, like fraud or tax evasion. Financial experts are practically a guaranteed element of any white-collar crime case. White-collar crimes are nonviolent crimes typically committed by business or government professionals for the purpose of stealing, or otherwise illegally coming into, large sums of money.

Forensic Expert

Forensic experts may be medical experts, but not always. Forensic experts’ strengths lie in the criminal acts themselves. For instance, blood spatter experts, psychologists, and criminal behavior experts can all be classified as forensic experts. Forensic experts are, more often than not, called upon as witnesses for the prosecution. However, the defense may call upon a forensic expert to poke holes in the prosecution’s case.

Vocational Expert

Vocational experts primarily stick to cases involving Social Security disability benefits at appeals hearings, though they may be used in workers’ compensation cases as well. These experts are typically called upon by the Social Security Administration to help determine whether the person applying for benefits is actually capable of going back to work, or if he is just trying to game the system.

Mental Health Expert

Mental health experts are similar to medical experts. The difference is that mental health experts testify as to whether the defendant is mentally sound. In other words, the expert can provide evidence showing whether the defendant is clinically insane, and whether he understood his actions and the consequences of them during the incident in question.

Expert Witness Example that Set the Standard in Using Expert Witnesses at Trial

Perhaps the most important example of an expert witness being used during a trial comes from the case of Daubert v. Merrell Dow Pharmaceuticals, Inc. This case is important because it set the standard on how expert witnesses are called to trial today. In fact, this case is the reason why the Daubert standard exists. The Daubert standard is a rule of evidence that determines whether an expert witness’ testimony is admissible as a form of evidence at trial.

Here, young boys Jason Daubert and Eric Schuller were born with birth defects that significantly affected their limbs. As a result, while Daubert and Schuller were still minors, their families took it upon themselves to sue Merrell Dow Pharmaceuticals. In the suit, the parties alleged that Daubert and Schuller’s mothers took a drug named “Bendectin” – manufactured by Merrell Dow – while pregnant and that, as a result, the boys suffered these severe birth defects.

Merrell Dow moved to have the case dismissed based on the fact that their expert witness submitted documents showing there was no scientific evidence that Bendectin caused birth defects. However, Daubert and Schuller provided their own expert evidence to prove that it did. The problem was, Daubert and Schuller’s evidence was gathered during studies that had not yet been accepted as viable within the scientific community.

Upon review, the California District Court awarded the dismissal, and Daubert and Schuller appealed. Their case then ended up before the Ninth Circuit Court of Appeals, which ultimately affirmed the lower Court’s decision. The Ninth Circuit agreed that the evidence provided by Daubert and Schuller could not be considered reliable evidence. The Ninth Circuit believed that, without the so-called “evidence” they had collected, Daubert and Schuller would otherwise be unable to prove that Bendectin was responsible for their birth defects.

Referring to the Federal Rules of Evidence, the Court held:

“The Rules — especially Rule 702— place appropriate limits on the admissibility of purportedly scientific evidence by assigning to the trial judge the task of ensuring that an expert’s testimony both rests on a reliable foundation and is relevant to the task at hand. The reliability standard is established by Rule 702’s requirement that an expert’s testimony pertain to ‘scientific… knowledge,’ since the adjective ‘scientific’ implies a grounding in science’s methods and procedures, while the word ‘knowledge’ connotes a body of known facts or of ideas inferred from such facts or accepted as true on good grounds. The Rule’s requirement that the testimony ‘assist the trier of fact to understand the evidence or to determine a fact in issue’ goes primarily to relevance by demanding a valid scientific connection to the pertinent inquiry as a precondition to admissibility.”

Related Legal Terms and Issues

  • Defendant – A party against whom a lawsuit has been filed in civil court, or who has been accused of, or charged with, a crime or offense.
  • Fraud – A false representation of fact, whether by words, conduct, or concealment, intended to deceive another.
  • Plaintiff – A person who brings a legal action against another person or entity, such as in a civil lawsuit, or criminal proceedings.
  • Prosecution – The lawyers who argue that an individual who is accused of a crime is guilty of that crime.
  • Retainer – A fee that is paid in advance to an individual to secure his services for the future.
  • Testimony – A declaration or statement of a witness under oath, usually in court.
  • Trial – A formal presentation of evidence before a judge and jury for the purpose of determining guilt or innocence in a criminal case, or to make a determination in a civil matter.