Also known as:FRE 703 · Fed. R. Evid. 703 · Federal Rule of Evidence 703 · Rule 703 · expert opinion bases
Written by attorneys · grounded in primary & secondary sources — see below
A rule of evidence that allows an expert to base an opinion on facts or data that experts in the field would reasonably rely on even if those facts or data are inadmissible.
Sources & Authorities
How it applies
Common Examples
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Expert Relies on Undisclosed Algorithm
Francisco Frost, a software engineer retained by Falcon Dynamics, reviewed only marketing brochures and selected code snippets supplied by counsel before concluding that a competitor had copied proprietary algorithms. He formed his opinion without examining complete source code or the underlying dataset for similarity scores generated by a proprietary tool. The court permitted the testimony because experts in the field reasonably rely on such materials when forming opinions about code infringement.
DNA Analyst Testifies on Profile Match
Fatima Flores, a forensic analyst, testified that a DNA profile from a crime scene matched a defendant after reviewing a report prepared by an outside laboratory. She had not personally conducted the testing or observed the sample handling but relied on the report's data as is customary in her field. The court allowed the opinion because the underlying facts were of a type reasonably relied upon by DNA experts.
Select any source to read its text and confirm it supports the definition.
Federal Rules
Casebooks
Williams v. Illinois567 U.S. 50 (2012)
Common questions
Frequently Asked
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What types of materials may an expert rely on under F.R.E. 703?+
An expert may rely on facts or data made known to the expert at or before the hearing if experts in the particular field would reasonably rely on those kinds of facts or data. The rule permits reliance on inadmissible materials when they are of the type customarily used in the expert's field.
Supporting sources
Does F.R.E. 703 require the expert to have personal knowledge of the underlying facts?+
No. Rule 703 expressly permits an expert to base an opinion on facts or data the expert did not personally observe or perceive. This stands in contrast to the personal-knowledge requirement of Rule 602 that applies to lay witnesses.
Supporting sources
When may a court exclude an expert opinion under F.R.E. 703?+
A court may exclude the opinion if the facts or data are not of a type reasonably relied upon by experts in the field or if their probative value is substantially outweighed by the danger of unfair prejudice. The rule does not allow an expert to serve as a conduit for inadmissible hearsay that lacks a reliable foundation.
Supporting sources
567 U.S. 50 (2012)Evidence
…opinion are not introduced for a plausible nonhearsay purpose”). This view is directly contrary to the current version of Rule 703 of the FederalRules of Evidence, which this Court approved and sent to Congress in 2000. Under that Rule, “basis evidence” that is not admissible for its truth may be disclosed even in a…
EvidencePresentation of evidence · Impeachment, contradiction, and rehabilitationUBEIntermediate