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 Louisiana, expert witness testimony is governed by the Louisiana Code of Evidence, particularly Article 702, which aligns with the principles described. An expert witness in Louisiana may be qualified based on their knowledge, skill, experience, training, or education, and can provide testimony if it offers scientific, technical, or other specialized knowledge that will help the court understand the evidence or decide on a contested fact. The determination of whether a witness is qualified as an expert does not follow a strict formula but requires a connection between the witness's expertise and the subject matter of the case. The judge serves as a gatekeeper, assessing the relevance and reliability of the expert's testimony before it is presented to the jury. This gatekeeping function is crucial to ensure that the expert evidence is not only pertinent but also adheres to standards of evidentiary reliability.