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.

In Tennessee, the admissibility of expert witness testimony is governed by rules similar to 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 relevant 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 fact that is in dispute. However, there is no strict formula for qualifying an expert witness. The key requirement is that there must be an appropriate match between the expert's expertise and the subject matter of the case. The determination of whether a witness is qualified as an expert is made by the trial judge, who serves as a gatekeeper to ensure that only reliable and relevant expert testimony is presented to the factfinder. This gatekeeping function is crucial to prevent unreliable or irrelevant expert evidence from influencing the outcome of the trial.