Federal Rule of Evidence 703 lets an expert base an opinion on “facts or data in the case that the expert has been made aware of” and not just facts or data that the expert has “personally observed.” The facts or data “need not be admissible” for the expert’s opinion to be admitted if “experts in the particular field would reasonably rely on those kinds of facts or data in forming an opinion on the subject.” Fed. R. Evid. 703.
Under Rule 703, courts routinely let experts testify based on otherwise inadmissible evidence, including the hearsay opinions of other experts or the work product of others who may or may not be experts. Technical experts often rely, necessarily, on the opinions of other experts with different expertise. In a nonlitigation context, experts may rely on research, surveys, or experiments performed by their own support teams or by third-party contractors when rendering professional services. In a litigation context, Rule 703 lets these experts rely on the same sources of information to support their courtroom testimony.
Notwithstanding Rule 703’s broad language, and despite the wide leeway that courts typically give experts under that rule, a number of important limitations exist to control its misuse. As a district judge in the Northern District of California has observed, “[o]ne of the worst abuses in civil litigation is the attempted spoon-feeding of client-prepared and lawyer-orchestrated ‘facts’ to a hired expert who then ‘relies’ on the information to express an opinion.” Therasense, Inc. v Becton Dickinson Co., No. C 04-02123 WHA, 2008 U.S. Dist. LEXIS 124780, at *13 (N.D. Cal. May 22, 2008). To curb such perceived abuses, courts may invoke a number of safeguards to prevent litigants from putting Rule 703 to illegitimate purposes.