Generally, there are different types of experts. Technical experts are usually scientists or engineers. Patent prosecution experts are usually patent attorneys or agents, and their testimony is scrutinized closely by the courts. Damage experts are usually accountants or other professionals who are capable of helping the court determine an appropriate award of damages.
It is often said that experts are the only witnesses who are allowed to give opinion testimony. However, this is not correct. Rule 701 of the Federal Rules of Evidence indicates that lay witnesses (i.e. witnesses who are not expert witnesses) may give opinion testimony that is:
“(a) rationally based on the perception of the witness, and (b) helpful to a clear understanding of the witness' testimony or the determination of a fact in issue, and (c) not based on scientific, technical, or other specialized knowledge within the scope of [another Federal Rule of Evidence that relates to expert testimony]."
The admissibility of lay opinion testimony is left to the discretion of the trial judge. Air Turbine Tech., Inc. v. Atlas Copco AB, 410 F.3d 701, 713 (Fed. Cir. 2005); Union Pacific Resources Co. v. Chesapeake Energy Corp., 236 F.3d 684, 692 (Fed. Cir. 2001).
The Union Pacific court permitted eight lay witnesses to present opinion testimony based upon their personal experiences in the oil drilling industry. Union Pacific, 236 F.3d at 693. Other courts have permitted lay witnesses to present opinion testimony based upon their personal experiences. See e.g., Plastics, Inc. v. Eastern Creative Industries, Inc., 2004 U.S. Dist. LEXIS 2311 *23-26 (S.D.N.Y. 2004); The Braun Corp. v. Maxon Lift Corp., 282 F.Supp.2d 931 (N.D. Ind. 2003), aff’d 2004 U.S. App. LEXIS 10851 (Fed. Cir. 2004)(nonprecedential).
Finally, experts are required to produce extensive reports that describe their credentials, their opinions and their methodology in arriving at those opinions prior to trial. These reports can be expensive and time consuming.