Rule 703: Bases of an Expert's Opinion Testimony

An expert may base an opinion on facts or data in the case that the expert has been made aware of or has personally observed. If experts in the particular field would reasonably rely on those kinds of facts or data in forming an opinion on the subject, they need not be admissible for the opinion to be admitted. But if the facts or data would otherwise be inadmissible, the proponent of the opinion may disclose them to the jury only if their probative value in helping the jury evaluate the opinion substantially outweighs their prejudicial effect.

• 1Experts can rely on inadmissible facts or data if experts in the field would reasonably rely on them
• 2Three bases: personal observation, facts presented at trial, and outside information provided to the expert
• 3Inadmissible underlying data may only be disclosed to the jury under a reverse-403 balancing test (probative value must substantially outweigh prejudice)
• 4The rule prevents experts from becoming a conduit for otherwise inadmissible hearsay

• Whether the expert's reliance on particular inadmissible information is reasonable for experts in that field
• The distinction between relying on inadmissible data (permitted) and disclosing it to the jury (restricted)
• Using an expert as a backdoor for hearsay — the rule's limiting instruction and reverse-403 test
• What constitutes 'facts or data' that experts in the field would 'reasonably rely' on