A witness who qualifies as an expert because of knowledge, skill, experience, training, or education may testify as an expert if scientific, technical, or other specialized knowledge will assist the judge, jury, or other factfinder to understand the evidence or determine a contested fact issue.

But there is no rigid formula for determining whether a particular witness is qualified to testify as an expert. Generally there must be a fit between the subject matter at issue and the expert witness’s familiarity with the subject matter. And this determination is made by the judge, who acts as a gatekeeper to only allow reliable expert witness testimony to be heard and considered by the judge or jury—and to exclude such testimony when it is not reliable.

In South Carolina, expert witness testimony is governed by rules similar to those found in the Federal Rules of Evidence. An individual may qualify as an expert witness if they possess specialized knowledge, skill, experience, training, or education that is pertinent to the case at hand. Their testimony is considered admissible if it provides assistance to the judge or jury in understanding the evidence or in determining a factual issue that is contested. The determination of whether a witness qualifies as an expert is not based on a strict formula but rather on the relevance and fit of the expert's knowledge to the subject matter of the dispute. The judge serves as a gatekeeper, ensuring that only reliable expert testimony is presented to the factfinder. This gatekeeping role involves assessing the methods and principles that underpin the expert's opinion, ensuring that the testimony is based on a reliable foundation and is relevant to the issues in the case. Expert testimony that does not meet these standards of reliability and relevance is excluded from consideration.