Expert testimony is a type of testimony that can be used in civil and criminal cases. In this article, we’ll define the term “expert testimony” and explain its requirements and types. We’ll also discuss the matter of who qualifies as an expert.

Key Takeaways

• Expert testimony is the testimony given in a trial or deposition by an expert witness on a usually scientific or technical subject
• In order for expert testimony to be admissible, it must meet several requirements, namely relevance, basis on facts, and application of reliable methods
• There are no specific criteria for who qualifies as an expert, and each potential expert witness must have their qualifications carefully scrutinized for relevance to the case at hand

What Is Expert Testimony?

Expert testimony is testimony given under oath in a trial or deposition by an expert witness on a subject relevant to a civil or criminal case. The subject of expert testimony is usually scientific or technical. Subjects often addressed in expert testimony include forensics, medicine, and ballistics.  

For context, it’s important to understand that generally, the law of evidence in both civil and criminal cases states that witnesses can only testify to concrete facts within their own observation, knowledge, and recollection. They are not meant to state conclusions drawn from facts of what they directly perceived. As such, opinions, inferences, impressions, and conclusions are usually not admissible evidence. Expert testimony is an exemption to this rule and can only be admitted if it meets very specific requirements.

According to the Federal Rules of Evidence, Rule 702, in order for expert testimony to be admissible, the following requirements must be met:

• The “expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue”
• “The testimony is based on sufficient facts or data”
• “The testimony is the product of reliable principles and methods” 
• “The expert has reliably applied the principles and methods to the facts of the case”

There are two types of matters in which expert testimony is considered relevant and admissible.

1. Matters as to which the conclusions to be drawn by the jury depend on facts that are not common knowledge. In this type of matter, the expert states the facts and the jury draws a conclusion. 
2. Matters as to which conclusions to be drawn depend on professional or scientific knowledge not within the range of ordinary training or intelligence. In this type of matter, the expert states the facts and draws a conclusion in the form of an opinion that the jury can accept or reject.

Who Qualifies as an Expert?

There is no specific rule determining whether a witness qualifies as an expert. Each expert’s qualifications must be evaluated and carefully scrutinized according to the relevant issues of that particular case. A common criterion is whether or not the jury can receive appreciable help from the expert’s testimony on a particular subject. 

Courts will often give extra scrutiny to the qualifications of would-be “experts” if they have never before given expert testimony in a court of law. However, the fact that a witness has previously served as an expert witness on a different case is not relevant to their qualification as an expert witness for a subsequent case.