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 Michigan, the admissibility of expert witness testimony is governed by Michigan Rule of Evidence 702, which aligns with the principles described. An expert witness is someone who has specialized knowledge, skill, experience, training, or education that can help the court understand evidence or determine a fact in question. The decision to qualify a witness as an expert rests with the judge, who serves as a gatekeeper to ensure that only relevant and reliable expert testimony is presented. The judge will consider whether the expert's knowledge is a good fit for the subject matter of the dispute and whether their testimony will provide valuable assistance to the judge or jury in resolving a contested issue. There is no strict formula for this determination; it is a discretionary judgment made by the court on a case-by-case basis, taking into account the expert's qualifications and the relevance of their expertise to the specific facts of the case.