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 New Hampshire, expert witnesses are permitted to testify in legal proceedings if their specialized knowledge, skill, experience, training, or education can help the court understand the evidence or decide on a contested fact. The state does not adhere to a strict formula for qualifying an expert witness. Instead, there must be a relevant connection between the expert's knowledge and the subject matter of the case. The determination of whether a witness is qualified as an expert is made by the presiding judge. This judge acts as a gatekeeper, ensuring that only reliable expert testimony is presented to the judge or jury. The judge's role is to assess the relevance and reliability of the expert's testimony, considering factors such as the methodology used and the potential for the testimony to aid in the understanding of the case.