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 Pennsylvania, the admissibility of 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 pertinent to the case at hand. The expert's testimony should provide assistance to the judge or jury in understanding complex evidence or in resolving a contested fact issue. However, there is no strict formula for qualifying an expert witness. The key requirement is that there must be a relevant connection between the witness's expertise and the subject matter of the dispute. The determination of whether a witness is qualified to testify as an expert is made by the presiding judge. This judge acts as a 'gatekeeper' to ensure that only reliable and relevant expert testimony is presented to the factfinder, whether it be the judge or jury. This gatekeeping function is crucial to maintaining the integrity of the proceedings and ensuring that the factfinder is not misled by unreliable expert evidence.