Evidence Act 2006

Admissibility rules, privilege, and confidentiality - Statements of opinion and expert evidence

25: Admissibility of expert opinion evidence

You could also call this:

"When can an expert's opinion be used as evidence in court?"

When you are in a court proceeding, an expert's opinion can be used as evidence if it helps you understand other evidence or figure out an important fact. The expert's opinion must be based on their area of expertise, and it can be about important issues in the case. You can still use the expert's opinion even if it is about something that most people know.

If an expert's opinion is based on a fact that is not part of their general knowledge, you can only use that opinion if the fact is proven or already known in the proceeding. This means the expert must have a good reason for their opinion, and that reason must be based on facts that are proven or well-known. The fact must be clear so you can trust the expert's opinion.

When an expert gives evidence about someone's sanity, they might rely on what that person told them about their state of mind. In this case, what the person said to the expert can be used as evidence to support the expert's opinion. The usual rules about hearsay do not apply to what the person said to the expert, so you can consider their statement when deciding the case.

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This page was last updated on 29 June 2025

View the original legislation for this page at https://legislation.govt.nz/act/public/1986/0120/latest/link.aspx?id=DLM393600.

Topics:

Crime and justice > Courts and legal help

24: General admissibility of opinions, or

"When you're a witness, you can share your opinion to help explain what happened"

26: Conduct of experts in civil proceedings, or

"Experts in court must follow the rules when giving evidence"

Part 2Admissibility rules, privilege, and confidentiality
Statements of opinion and expert evidence

25Admissibility of expert opinion evidence

An opinion by an expert that is part of expert evidence offered in a proceeding is admissible if the fact-finder is likely to obtain substantial help from the opinion in understanding other evidence in the proceeding or in ascertaining any fact that is of consequence to the determination of the proceeding.
An opinion by an expert is not inadmissible simply because it is about—
an ultimate issue to be determined in a proceeding; or
a matter of common knowledge.

If an opinion by an expert is based on a fact that is outside the general body of knowledge that makes up the expertise of the expert, the opinion may be relied on by the fact-finder only if that fact is or will be proved or judicially noticed in the proceeding.
If expert evidence about the sanity of a person is based in whole or in part on a statement that the person made to the expert about the person’s state of mind, then—
the statement of the person is admissible to establish the facts on which the expert’s opinion is based; and
neither the hearsay rule nor the previous consistent statements rule applies to evidence of the statement made by the person.

Subsection (3) is subject to subsection (4).