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 Arizona, expert witnesses are individuals who, due to their knowledge, skill, experience, training, or education, may provide testimony in legal proceedings if their insights can help the judge or jury understand the evidence or resolve a disputed fact. The decision to qualify someone as an expert witness does not follow a strict formula; instead, it requires a clear connection between the witness's expertise and the subject matter of the case. The judge serves as a gatekeeper, determining the admissibility of expert testimony to ensure that it is reliable and relevant to the case at hand. This gatekeeping role is crucial to prevent unreliable or irrelevant expert opinions from influencing the outcome of a trial. The judge's evaluation of an expert's qualifications and the applicability of their testimony to the case is guided by rules of evidence and case law.