Opinion and Expert Evidence

Question 1

76 – The opinion rule

Answer 1

Evidence of an opinion is not admissible to prove the existence of a fact about the existence of which the opinion was expressed.

The EA does not define ‘opinion’. The common law definition is ‘an inference drawn from observable fact’ )or ‘an inference drawn from observed and communicable data’ (Lithgow City Council v Jackson (2011).

Evidence of opinion (‘inferential’) may be distinguished from evidence of an experience (‘experiential’). Statement of own state of mind not an opinion; statement of another’s state of mind is an opinion.

Question 2

77 Exception: evidence relevant otherwise than as opinion evidence

Answer 2

Evidence of an opinion is admissible if it is relevant for a purpose other than proof of the existence of a fact about the existence of which the opinion was expressed.

If opinion evidence is admitted for another purpose, it may also be used to prove the facts about which the opinion is expressed (as with the hearsay rule).

SO: once in for non-opinion purpose, can use for opinion purpose

Question 3

78 Exception to opinion rule: lay opinions

Answer 3

Evidence of a lay opinion is excepted from exclusionary opinion rule if it is:

1. based on what the person saw, heard or otherwise perceived about a matter or event (s78(a)); AND
2. necessary to obtain an adequate account or understanding of the person’s perception of the matter or event (s78(b)).

Question 4

78A Exception to the opinion rule: ATSI traditional laws and customs

Answer 4

Evidence of an opinion about the existence or non-existence, or the content, of the traditional laws and customs of an ATSI group is not excluded if the opinion:

• is relevant (ss55-56); and
• is expressed by a member of that group.

Question 5

79: Exception for expert opinion - opinions based on ‘specialised knowledge’

Answer 5

If a person has specialised knowledge based on the person’s training, study or experience, the opinion rule does not apply to evidence of an opinion of that person that is wholly or substantially based on that knowledge.

Evidence must therefore satisfy three criteria to be admissible under the expert opinion exception:

1. witness must have specialised knowledge;
2. that knowledge is based on training, study or experience; AND
3. their opinion must be wholly or substantially based on that knowledge.

Expertise must be established by above criteria for EACH OPINION GIVEN. Determined on BOP (s142).