LAW4323 Chap.10 Opinion Evidence
Opinion Evidence
The opinion rule generally excludes an opinion offered to prove the fact expressed. Lay opinion can communicate perception through a defined exception, while expert opinion requires a specialised body of knowledge acquired through training, study or experience and reasoning that connects that knowledge to the conclusion. Credentials alone do not establish the statutory basis.
What this chapter covers
- 01
Fact and opinion
- 02
Lay perception
- 03
Specialised knowledge
- 04
Qualifications
- 05
Assumptions
- 06
Expert reasoning
Worked example · free
Test an image comparison
- 3Identify the identity opinion.
- 1Specify field and observed features.
- 1Demand reasoning based on specialised knowledge.
Key terms
- Opinion rule
- The general exclusion of opinion tendered for its conclusion.
- Lay opinion
- An inference based on personal perception.
- Specialised knowledge
- Knowledge gained through training, study or experience.
- Factual assumption
- An evidentiary input to expert reasoning.
Opinion Evidence FAQ
Are qualifications enough for expert evidence?
No. The opinion must be wholly or substantially based on specialised knowledge, with a disclosed path from facts and assumptions through reasoning to the stated conclusion.
What supports a lay-opinion exception?
The witness must rely on personal perception, and the opinion must be necessary to communicate adequately what the witness observed or experienced in the relevant circumstances.
How should an expert report be unpacked?
Separate observations, assumptions, methodology, intermediate reasoning and conclusion. Embedded representations may also require their own hearsay analysis and proof route before the opinion is admitted.
Exam move
Revise opinion evidence by decomposing every conclusion. Underline the evaluative words, write the fact the opinion is offered to prove, and list the observations or assumptions from which it was drawn. Decide whether the expression is ordinary fact description, lay shorthand or specialised opinion.
For lay witnesses, record the personal perception and explain why the evaluative form is needed to communicate what was perceived. Compare statements such as a person appeared angry, a vehicle travelled fast and a signature looked familiar. Change the witness's opportunity to observe and decide whether the problem concerns the exception, relevance or weight.
For expert evidence, build a five-column table: field of specialised knowledge, qualification through training, study or experience, facts and assumptions, method, and inferential reasoning. Credentials occupy only one column. Practise reports in which the expert is highly qualified but fails to connect the knowledge to the conclusion.
Identify whether the gap prevents section 79 from applying or limits the scope of the opinion. Separate observations, calculations, assumed facts, intermediate conclusions and ultimate opinion within a report. Mark embedded hearsay and decide how the underlying facts will be proved. When assumptions change, explain whether the reasoning still supports the same result.
Avoid relying on the ultimate-issue slogan; apply the statutory exception and ask whether the opinion assists with a specialised inference while leaving legal judgment to the court. Create cross-examination questions targeted to distinct weaknesses: qualification, data quality, assumption, methodology, application or scope. Do not describe every disagreement as lack of expertise.
During a timed answer, identify opinion and fact to prove first, state the general rule, name the exception and demonstrate basis. If reasoning is missing, say what connection must be shown rather than declaring the witness unqualified. Consider any discretionary issue only after classification.
Review each expert paragraph by removing the expert's title and asking whether the reader can still see why specialised knowledge produced the conclusion. If not, the reasoning is incomplete. Finish practice by comparing two experts who share data but use different assumptions or methods. Explain whether the conflict affects admissibility or weight.
This disciplined decomposition prevents an impressive report format from hiding unsupported inference and helps distinguish a genuine specialist bridge from ordinary visual comparison or speculation.
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