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 Connecticut, the admissibility of expert witness testimony is governed by the principles that the expert must have knowledge, skill, experience, training, or education that is pertinent to the subject matter of the case. The expert's testimony should provide assistance to the judge or jury in understanding the evidence or in making a determination on a contested fact. The judge serves as a gatekeeper, ensuring that only reliable expert testimony is presented. This means that the judge must evaluate whether there is an appropriate fit between the expert's qualifications and the specific issues at hand in the case. The reliability of the expert's methods and the applicability of their expertise to the facts of the case are critical factors in this determination. Connecticut follows the standards set forth in the Federal Rules of Evidence and relevant case law, which do not prescribe a strict formula for qualifying an expert witness but rather emphasize the importance of relevance and reliability of the expert's testimony.