Lay vs. Expert Witness

What is the difference between a lay witness and an expert witness?  The Federal Rules of Evidence governing lay opinions and expert testimony are rules 701 and 702.  These rules detail the standards for admissibility of evidence.

Lay witness opinions are inadmissible, unless:  (1) rationally based on the witness’ perception, and (2) helpful to a clear understanding of the testimony or determination of a fact in issue.

Lay opinions usually do not need to be disclosed before trial or supported by formal reports.  If attorneys are not sure whether they need to disclose lay witness opinions when required under state law, they can have an agreement with opposing counsel as to the disclosures required for specific testimony for the case.

Federal circuit courts have different conclusions on the scope of permissible lay opinion testimony. Some courts take a broad view. For example, in U.S. v. Jayyousi, 657 F.3d 1085 (11th Cir. 2011), the Eleventh Circuit allowed an FBI agent to testify as to the meaning of alleged code words used between codefendants, although the calls were mostly in Arabic and the agent did not speak the language. Id. at 1101–1104. Some courts take a narrow view.  For example, the Sixth Circuit in U.S. v. Freeman, 730 F.3d 590 (6th Cir. 2013) reversed and remanded a trial court’s decision to allow an FBI agent’s lay witness testimony.  The testimony interpreted phone calls between codefendants when the agent gave voice identifications and substantive interpretations of the meaning of statements contained in the calls.

A person may testify as an expert (state an opinion or conclusion) if s/he (1) has scientific, technical, or specialized knowledge that will assist the trier of fact, (2) qualifies as an expert in the field, (3) possesses reasonable probability regarding his/her opinion, and (4) supports the opinion with a proper factual basis.  These expert witness requirements come from U.S. Supreme Court in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993).

There are disclosure requirements for relying on expert testimony when a case is in federal court.  Federal Rule of Civil Procedure 26(a)(2) requires expert reports from retained experts. Disclosures ensure that testimony that counsel relies on is not excluded before trial.

An understanding of how a specific court interprets the scope and requirements for lay opinions and expert witness testimony is necessary when a personal injury or medical malpractice attorney develops case strategy.