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 New Mexico, as in many jurisdictions, the admissibility of expert witness testimony is governed by rules that require the testimony to be both relevant and reliable. An expert witness, as defined by their knowledge, skill, experience, training, or education, may be permitted to testify if their specialized knowledge will help the court understand the evidence or a fact in dispute. 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 their expertise in relation to the subject matter of the case. The judge serves as a gatekeeper, assessing the appropriateness of the expert's testimony, ensuring that it is sufficiently tied to the issue at hand and based on a reliable foundation. This gatekeeping role is crucial to prevent unreliable expert testimony from influencing the judge or jury. The specific rules and standards for expert witness testimony in New Mexico are aligned with the federal rules and can be found in the New Mexico Rules of Evidence.