In our last lesson in our ongoing series, Tips for Testifying in Legal Proceedings, we looked at the differences between lay witnesses and expert witnesses, and pointed out that a lay witness on the stand can generally only testify about facts, while an expert witness can testify regarding the opinions or conclusions he or she draws from those facts.  Today, we’ll look more closely at expert witnesses, to learn what makes a person an expert witness and what kind of testimony they can give.

Lesson 6: Who Is Qualified to Testify as an Expert

Just because a person is an expert in a particular field does not necessarily mean they are legally considered an expert.  The legal system has a specific set of guidelines to determine when a person is an expert witness who can give opinion testimony.

What is an Expert Witness?

An expert witness is allowed to provide a scientific, technical, or other specialized opinion about the evidence or a fact issue based upon their qualifications, knowledge, skill, experience, training, or education.  The rationale behind this is that the opinion of a person with specialized training or education, such as a scientist, will be of more value to the judge and jury in deciding the case.Expert witnesses are persons who are qualified, either by actual experience or by careful study, to form definite opinions with respect to a division of science, a branch of art, or a department of trade. The law deems persons having no such experience or training to be incapable of forming accurate opinions or drawing correct conclusions. Thus, if scientific, technical, or other specialized knowledge will assist the trier of fact (the judge or jury) to understand the evidence or to determine a fact in issue, a witness who has been qualified as an expert may testify in the form of an opinion or otherwise.  To allow the expert testimony, three criteria must be met: (1) the testimony is based upon sufficient facts or data; (2) the testimony is the product of reliable principles and methods; and (3) the witness has applied the principles and methods reliably to the facts of the case.

Qualifying an Expert Witness

Courts do not apply a rigid rule in determining whether a particular witness is qualified to testify as an expert. Instead, an expert’s qualifications are normally evaluated on a witness-by-witness basis, according to the facts and issues of each case. The process of determining that a particular person is permitted to give expert testimony is known as “qualifying” the witness.Several courts have stated that the true criterion in determining the qualification of expert witnesses is not whether they employ their knowledge and skill professionally or commercially, but whether the jury can receive appreciable help from them on the particular subject in issue. Many courts also require the witness to exhibit sufficient knowledge of the subject matter before his or her opinion to go to the fact finder (the judge or jury).The qualifications of an expert witness must be carefully scrutinized by courts to guard against charlatans who may give erroneous testimony without a sound foundation, thus misleading the judge or jury. Most courts will more closely scrutinize the qualifications of witnesses seeking to testify as experts if they have never been found qualified to give expert testimony on a prior occasion. However, primary reliance is not placed on the fact that it may be the expert’s first time on the witness stand. Conversely, the fact that a witness has been previously qualified to give expert testimony on the subject matter in question is typically irrelevant to his or her qualifications for giving expert testimony in a subsequent case.

Kinds of Expert Testimony

There are two general classes of matters as to which expert testimony is admissible: (1) matters as to which the conclusions to be drawn by the jury depend on the existence of facts that are not common knowledge and that are specifically within the knowledge of persons whose experience or study enables them to testify with authority on the subjects in question; and (2) matters as to which the conclusions to be drawn from the facts stated, as well as knowledge of the facts themselves, depend on professional or scientific knowledge not within the range of ordinary training or intelligence. In the first class, the facts are stated by the experts, and the conclusion is drawn by the jury. In the second class, the expert sets forth the facts and states a conclusion in the form of an opinion which may be accepted or rejected by the judge or jury.Expert testimony can be extremely useful to the judge and jury as they try to make legal decisions on topic they may not be familiar with.  However, it is essential that courts make sure an expert is properly qualified before he or she gives testimony on their opinions or conclusions.Next time: we’ll talk about how to recognize and avoid dual roles, in 10 Essential Differences Between a Therapeutic and a Forensic Relationship.