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 Jersey, the admissibility of expert witness testimony is governed by the New Jersey Rules of Evidence, specifically Rule 702. This rule allows a witness who has specialized knowledge, skill, experience, training, or education to testify in the form of an opinion or otherwise if their expertise will help the judge or jury understand the evidence or decide a fact in question. 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 witness's expertise in relation to the subject matter of the dispute. The judge serves as a gatekeeper, ensuring that only expert testimony that is pertinent and reliable is presented to the factfinder. This gatekeeping function is consistent with the standards set by the New Jersey Supreme Court in cases such as State v. Kelly and Landrigan v. Celotex Corp., which reflect a commitment to ensuring that expert testimony is based on a methodology that can be deemed trustworthy and is properly applied to the facts of the case.