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 West Virginia, the admissibility of expert witness testimony is governed by rules that are similar to those found in the Federal Rules of Evidence. An individual may testify as an expert if they have the requisite knowledge, skill, experience, training, or education that is pertinent to the subject matter of the case. The expert's testimony should provide assistance to the judge or jury in understanding the evidence or in making a determination on a contested fact. The judge serves as a gatekeeper, ensuring that only relevant and reliable expert testimony is presented. This involves assessing whether there is an appropriate fit between the expert's expertise and the subject matter at issue. The judge's role is to exclude expert testimony that does not meet the standards of reliability and relevance, ensuring that the factfinder is not misled by information that does not have a sound basis in knowledge and methods that are accepted by the relevant scientific community.