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 Idaho, expert witness testimony is governed by the Idaho Rules of Evidence, specifically Rule 702. This rule allows a witness who has knowledge, skill, experience, training, or education that qualifies them as an expert in a particular field to provide testimony if it will help the court understand the evidence or determine a fact in issue. The determination of whether a witness is qualified as an expert is not based on a strict formula but rather on whether there is an appropriate fit between the witness's expertise and the subject matter at hand. The judge serves as a gatekeeper, assessing the reliability of the expert's testimony and deciding whether it should be admitted for consideration by the jury or the judge in a bench trial. The judge's role is to ensure that the expert testimony is not only relevant but also reliable, based on a sufficient factual or data foundation, and that the expert has applied the principles and methods reliably to the facts of the case.