An adverse party can’t require a witness to start with the basis for his or her opinion, that’s left to the trial judge’s discretion. See Evid C §802.
But an adverse party can nudge the trial judge into requiring it of a witness in two ways:
- Use an objection to raise the issue. If an adverse party objects to a question that asks a witness to state an opinion, on the ground that the witness has not first stated the matter relied on, the judge may sustain the objection and require the direct examiner to examine the witness on the facts on which the opinion is based.
- Ask to voir dire the witness. An adverse party may raise the point by making a request to voir dire the witness before he or she is permitted to answer the direct examiner’s question about his or her opinion. If the trial judge grants the request, the adverse party may then conduct a voir dire examination of the witness about the matter relied on by the witness in forming his or her opinion.
Why would a judge require a witness to first testify to the matter relied on before stating an opinion? Usually it’s to determine whether the opinion is based on proper or improper matter. A witness who has formed an opinion wholly, or in substantial part, on improper matter, such as speculative or conjectural material, or on unreliable hearsay, may not testify to that opinion. See Evid C §§800–801.
Get more expert advice for handling opinion testimony in CEB’s Jefferson’s California Evidence Benchbook, chap 30.
Other CEBblog™ posts you may find useful:
- Techniques Top Attorneys Use When Questioning an Expert
- Can Opinion Come In Under the Business-Records Exception?
- Questioning a Witness: Poor Questions Versus Good Ones
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