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Admissibility of Expert Testimony

Admissibility of Expert Testimony

Forensic expert witnesses need to know the rules of evidence.

“Learn how Rule 702 of Federal Evidence, embraces the Daubert principal and rejects “junk science.”

Forensic engineering is defined by the National Academy of Forensic Engineers (NAFE) as “the application of the art and science of engineering in matters which are in, or may possibly relate to, the jurisprudence system, inclusive of alternative dispute resolution.” These engineers serve as consultants to the legal profession and as expert witnesses in courts of law.


Forensic engineers need to understand the rules that apply to their testimony in the jurisdiction of the court. The following is included in the 2014 Federal Rules of Evidence:

Rule 702. Testimony by Expert Witnesses

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if: (a) the expert’s scientific, technical, or other specialized knowledge will help the “trier of fact” [Jury & or Judge] to understand the evidence or to determine a fact in issue;(b) the testimony is based on sufficient facts or data;(c) the testimony is the product of reliable principles and methods; and(d) the expert has reliably applied the principles and methods to the facts of the case.

This federal requirement, embraces the Daubert rule. If the testimony is based on a “novel theory”, this rule requires the judge to determine if it is sufficiently supported to qualify as evidence or it should be dismissed as “junk science”.

The Us Supreme Court has provided guidance tor trial courts by providing the following list of some of the factors that may be considered in evaluating admissibility of evidence.

  1. Empirical testing: whether the theory or technique is falsifiable, refutable, and/or testable.
  2. Whether it has been subjected to peer review and publication.
  3. The known or potential error rate.
  4. The existence and maintenance of standards and controls concerning its operation.
  5. The degree to which the theory and technique is generally accepted by a relevant scientific community.

Comparable rules have been adopted in many states. However, some states still use the older Frye rule, under which publication in a peer journal is usually sufficient; assurances by the expert witness are not adequate. If you are not testifying in federal court, it incumbent upon you to verify with your attorney-client the requirements of the court of venue.


The following is a narrative synopses of one of my cases. This is not intended to be a formal presentation of legal actions. No confidential or privileged information is revealed. This is simply my recollection, intended only to illustrate an expert’s typical involvement in judicial matters.

I was the chief investigator and expert witness on all of the forensic cases of Gaskell Associates, Ltd., and later those of the Gaskell Associates division of Thielsch Engineering until my retirement. However, it was my practice to meet on each case with my senior staff to “brainstorm” the case. This often opened up avenues of investigation that had not previously occurred to me. I attribute much of my success to hiring others who are smarter than I am.

Example Case – Power Line Proximity to Structure

An interesting case involved “Ozzie” the roofer. Part of my job was to read his “deposition,” his fact witness statement of what he observed. Ozzie was hired to put a new rubber roof on a tenement. Near the completion of the project, he was attaching the 10-foot metal edge strips. As he was nailing a strip to the edge, he saw another strip start to blow off the roof and reached out to grab it. In doing so, he extended it out into contact with a 25,000 volt distribution line. Current flowed through the metal edge strip, through Ozzie’s right hand, through his left hand that was still holding the other edge strip, down the aluminum siding on the building facade and then damaged all the appliances in the first-floor pizza restaurant.

The attorney asked him how he felt. “I was a little tired, so I took the rest of the day off”, Ozzie told him. Some things cannot be explained; perhaps Ozzie has a guardian angel. Incidentally, Ozzie was not even a party to the lawsuit; the pizza guy was trying to collect for his appliances.


Litigation consulting is interesting, challenging, and profitable. If what is involved interests you, I recommend adding “Forensic Engineering” to your practice as a consulting engineer. Get Jack’s new book: The “Complete Guide” to FORENSIC ENGINEERING to learn the details. Also, the largest chapter in his book: The “Complete Guide” to CONSULTING ENGINEERING covers the “highlights of Forensic Engineering. Visit to find out more.

Learn how to be a forensic engineer. Learn how to be a forensic expert witness. How to be an engineering expert witness. How to obtain training as a forensic engineer. How to obtain training as an engineering expert witness.