Rule 705 Disclosure of Facts or Data Underlying Expert Opinion

• Jurisdiction: Arizona

The expert may testify in terms of opinion or inference and give reasons therefor without prior disclosure of the underlying facts or data, unless the court requires otherwise. The expert may in any event be required to disclose the underlying facts or data on cross-examination.

Comment

This rule eliminates the necessity for hypothetical questions except when required by the court. The party calling the expert witness may elicit the underlying facts or data prior to obtaining an expert's opinion, but is not required to do so unless the trial court so orders.

An expert witness who bases an opinion on facts not admitted in evidence may disclose these facts if they are of the type upon which experts reasonably rely, and may disclose them on direct examination.[1] If the party calling the expert witness does not ask the expert to disclose the underlying facts on direct examination, the opposing party may do so on cross-examination.[2] The party cross-examining the expert is not required to ask the expert to disclose all the facts, and may instead ask questions designed to bring out only those facts or data unfavorable to the opinion. This assumes that the opposing party has obtained the advance knowledge necessary for effective cross-examination, through discovery provided in Arizona Rules of Civil Procedure, depositions, or by other means of discovery. The witness may disclose the facts or data upon which the witness relied, but only for the limited purpose of disclosing the basis of the opinion and not as substantive evidence.[3]

Although this rule allows for the disclosure of facts or data not admissible in evidence to the extent allowed by Rule 703, the trial court should exercise caution in its use so that it is not used merely as a guise to introduce otherwise inadmissible evidence.[4] For example, if an expert witness relies upon facts or data contained in a report not admitted in evidence, the trial court should allow the witness to disclose the facts or data, but should not admit the report itself because the report would still be hearsay. If the trial court admits such facts or data, a party would be entitled to an instruction under Rule 105 that the evidence is admitted only to show the basis for the opinion and not as substantive evidence.

Cases

705.010 An expert witness who bases an opinion on facts not admitted in evidence may disclose these facts if they are of the type upon which experts reasonably rely, and may disclose them on direct...