LAWS50037 · Evidence And Proof
Opinion Evidence
Opinion evidence answers a narrow question: can a witness give an inference, not just what they perceived? The rule is no (s 76 — the opinion rule) unless the witness is giving a lay opinion grounded in their own perception (s 78) or an expert opinion based on specialised knowledge (s 79). The whole battle in s 79 is the basis rule: there must be a genuine field of specialised knowledge, the witness must have it, and the opinion must be wholly or substantially based on it — with the assumptions and reasoning exposed and applied to proved facts (Dasreef v Hawchar). Honeysett v The Queen warns that subjective impressions are not specialised knowledge. There is no separate reliability requirement at s 79 — reliability bites later, at s 137. Note too that an expert’s report is usually a previous representation, so opinion is a cumulative rule, like hearsay: the clean exam move is to have the expert testify live, curing hearsay, then litigate s 79.
What this chapter covers
- 01s 76 — the opinion rule
- 02s 77 — the non-opinion-purpose exception
- 03s 78 — lay opinion (the two-element test: perception + necessity)
- 04s 79 — expert opinion and the basis rule
- 05s 80 — ultimate-issue & common-knowledge rules abolished
- 06Dasreef · Honeysett · HG · Makita — the leading cases
- 07Opinion as a cumulative rule with hearsay
Worked example: does the expert opinion satisfy s 79?
- +1State the asserted fact (s 76). The opinion is led to prove identity — that the offender is the accused. As an opinion, s 76 makes it inadmissible unless an exception applies.
- +1Lay or expert? It is offered as expert, so test s 79: (i) a genuine field of specialised knowledge; (ii) the witness has it; (iii) the opinion is wholly or substantially based on it; (iv) it is communicated in enough detail to be evaluated.
- +1Apply the basis rule (Dasreef). The assumptions and reasoning must be exposed and applied to proved facts. A bare conclusion (‘walks like the accused’) without exposed reasoning fails the basis rule.
- +1Apply Honeysett. Where the opinion rests on the witness’s subjective impression of the footage rather than her specialised knowledge, it is not based on specialised knowledge — so s 79 is not satisfied.
- +1Conclude (and note s 137). The opinion is inadmissible under s 79 as framed; even a properly-based version would still face s 137 reliability/prejudice exclusion in a criminal trial.
Key terms
- Opinion rule (s 76)
- Evidence of an opinion is not admissible to prove the existence of a fact about which the opinion was expressed. An ‘opinion’ is an inference drawn from observed and communicable data (Lithgow City Council v Jackson).
- Lay opinion (s 78)
- An exception with a two-element test: the opinion must be (a) based on what the person saw, heard or otherwise perceived, and (b) necessary to obtain an adequate account of that perception — e.g. speed, age, identity, emotional state, intoxication.
- Expert opinion (s 79)
- An exception where a person has specialised knowledge from training, study or experience, and the opinion is wholly or substantially based on that knowledge. s 79(2) expressly includes specialised knowledge of child development and behaviour.
- The basis rule
- The heart of s 79 (Dasreef v Hawchar; Heydon JA in Makita): the field, the witness’s knowledge and the reasoning from proved facts must all be exposed, so the opinion can be evaluated. The factual assumptions relied on must themselves be proved by admissible evidence.
- Honeysett v The Queen (2014)
- Subjective impressions are not specialised knowledge: an opinion dressed up as expertise but really resting on the witness’s untested impression of footage does not satisfy s 79.
Opinion Evidence FAQ
How do I tell lay opinion from expert opinion?
By the source of the inference. A lay opinion (s 78) is grounded in the witness’s own perception and is necessary to convey it — everyday inferences like ‘he seemed drunk’ or ‘the car was going fast’. An expert opinion (s 79) is grounded in specialised knowledge from training, study or experience. The exam move is to state the asserted fact (s 76), then pick the right exception and run its specific test.
What is the basis rule and why does it decide most s 79 questions?
The basis rule requires the expert to expose the field, their knowledge of it, and the reasoning that connects proved facts to the opinion, so the tribunal can evaluate it (Dasreef; Makita). A bare conclusion fails it. Crucially, the factual assumptions the expert relies on must themselves be proved by admissible evidence — if they are not, the opinion has no basis. Most s 79 battles are won or lost here.
Is there a reliability requirement in s 79?
No separate one. Section 79 does not impose a standalone reliability test — that was deliberate. Reliability concerns bite later, at s 137 (and s 135), where unreliable expert evidence with limited probative value can be excluded for unfair prejudice. So in a criminal trial, ‘the science is shaky’ is usually a s 137 argument, not a s 79 one.
Why is opinion called a cumulative rule?
Because an out-of-court expert report is usually also a previous representation, so it must clear both the hearsay rule and s 79. Clearing s 79 does not cure hearsay, and vice versa. The clean exam move is to have the expert testify live, which cures the hearsay problem, and then litigate s 79 on the live evidence. The same cumulative logic links opinion to tendency and the discretions.
Exam move
For every opinion in a brief, write the asserted fact it is led to prove (s 76), then branch: lay (s 78, perception + necessity) or expert (s 79). For s 79 run the four-part checklist — a genuine field, the witness has it, the opinion is wholly/substantially based on it (the basis rule, with assumptions proved), and it is communicated in enough detail to evaluate. Keep Dasreef (basis rule) and Honeysett (subjective impression is not specialised knowledge) on a tab. Remember the two structural points that win marks: there is no separate reliability test at s 79 (reliability is s 137), and opinion is cumulative with hearsay, so have the expert testify live.
