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 Wisconsin, expert witness testimony is governed by state statutes and case law. An individual may qualify as an expert witness if they possess specialized knowledge, skill, experience, training, or education that is relevant to the case at hand. Their testimony is considered valuable if it can help the judge or jury understand the evidence or resolve a contested fact. However, there is no strict formula for determining who qualifies as an expert. The key factor is the relevance and reliability of the expert's knowledge to the subject matter of the dispute. The judge serves as a gatekeeper, assessing the admissibility of the expert's testimony. The judge must ensure that the testimony is not only relevant but also reliable, based on a valid scientific, technical, or specialized foundation. This gatekeeping role is crucial to prevent unreliable expert testimony from influencing the outcome of a trial. The standards for expert witness admissibility in Wisconsin are influenced by both the Federal Rules of Evidence and state-specific precedents.