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 Maine, as in many jurisdictions, the admissibility of expert witness testimony is governed by rules that allow individuals with specialized knowledge, skill, experience, training, or education to provide expert testimony if it will help the court understand the evidence or a disputed fact. The determination of whether a witness qualifies as an expert is not based on a strict formula but rather on the relevance and reliability of the expert's knowledge in relation to the subject matter of the case. The judge serves as a gatekeeper, assessing whether the proposed testimony is pertinent and whether the witness has the appropriate qualifications to address the specific issues in the case. This gatekeeping role involves ensuring that the expert's methods are reliable and that their expertise directly applies to the matters at hand, in accordance with the Maine Rules of Evidence and relevant case law.