Lay Witness vs. Expert Witness Opinions: A Primer

Environmental Law, Regs, Litigation, State & Federal

Date posted: 12/30/16

Anjelica Cappellino reports that at common law, lay witnesses could testify to facts, but unlike experts, could not offer opinions, inferences, or conclusions. The justification was that unless information was too complex for a jury to understand without the help of an expert, a jury should be able to interpret evidence and draw its own conclusions. However, as the Supreme Court has noted, there is an inevitably arbitrary line between the various shades of fact and opinion. Once Rule 701 of the Federal Rules of Evidence was enacted, the restrictions on lay opinions began to loosen. Now, both lay and expert opinions are admissible at trial, to varying degrees. In order to ensure that your expert testimony is utilized to its full potential, it is important to note the differences between the two types of witnesses so that both can offer admissible opinions. Lay opinion testimony is largely defined by what it is not, expert testimony. Under Rule 702, 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 scientific, technical, or other specialized knowledge will help the trier of fact 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. In contrast, Rule 701 of the Federal Rules of Evidence states that if a witness is not testifying as an expert, testimony in the form of an opinion is limited to one that is... a) rationally based on the witness perception, b) helpful to clearly understanding the witness testimony or to determining a fact in issue, and c) not based on scientific, technical, or other specialized knowledge within the scope of Rule 702. The major difference between these two types of witnesses is personal knowledge.