There are many hurdles facing the admissibility and acceptance of expert evidence. The general opinion rule provides that “if a person has specialised knowledge based on the person’s training, study or experience” the opinion is admissible. However, often forgotten, is the Court’s general discretion to exclude evidence which is either prejudicial or irrelevant. Even if your expert satisfies the opinion rule, the evidence risks being excluded at any time. Therefore, it is critically important to understand the effect and operation of the discretion to exclude, supplemented with case examples.
The General Discretion to Exclude
The general discretion to exclude expert evidence is contained within s135 of the Evidence Act, which provides:
The court may refuse to admit evidence if its probative value is substantially outweighed by the damage that the evidence might:
- Be unfairly prejudicial to a party; or
- Be misleading or confusing; or
- Cause or result in ‘undue waste of time’
The section is discretionary and may be invoked at any time. Effectively, an experts report can be excluded even during a hearing leaving a case potentially dead in the water. In Australia, this has happened time and time again.
For example, in Haissam Assatini v The Shell Company of Australia an expert architect prepared a report dealing with the integrity of a commercial building structure. McDougall J excluded the evidence under s135 and held that “the total want of any rational reasoning process requires that the report be rejected under s135. Further, it is entirely inappropriate to put on a report that is totally devoid of any rational process of reasoning”.
Again, in Singh v Newridge Property Group Pty Ltd, evidence that was adduced at short notice was excluded on the basis that the other side would have to adduce evidence in reply leading to an adjournment of the proceedings.
Given the potential for exclusion therefore, expert evidence should be relevant, obtained well in advance and supported by a logical chain of reasoning. It is instructive in this regard to remember the six point formula to the relevance of expert opinions laid down by the High Court in Dasreef v Hawchar, that is:
- The opinion has to be on an area that the court accepts is an area of specialised knowledge;
- The witness must demonstrate that by reason of specified training, study or experience they are an expert in that area;
- The opinion must be on matters within that area of expertise;
- The expert must state, and the party calling the expert must prove, the facts on which the expert opinion is based;
- If any facts relevant to the opinion are assumed they must be identified and proved in some other way; and
- The expert must explain how the opinion expressed was reached.
This formula should be referred to and any expert evidence obtained should be cross checked to assess its probity.
One of the other grounds for exclusion under s135 is where the evidence poses an ‘undue waste of time’. This even extends to matters where the evidence could critically affect the case at hand. In Dyldam Developments Pty Ltd v Jones a party sought to make use of a document which it itself had previously failed to produce in response to the other sides valid subpoena. The document was highly relevant to the facts in issue however the Court of Appeal held that the plaintiff would have had to spend a lengthy amount of time digesting the document and would require an adjournment leading to a waste of Court’s resources. On that basis, the undue waste of time substantially outweighed the probative value and it was excluded.
Misleading or Confusing Evidence and Relevance
The final way in which the discretion operates is to allow for the exclusion of irrelevant expert material. The usual test of relevance applies, that is to say, evidence which could rationally affect the probability or improbability of the fact in issue. Matters which are known to the world or so obvious that they go without saying are also irrelevant.
A good illustration of this issue is the well-publicised case of Cadbury Schweppes Pty Ltd v Darrell Lea Chocolate Shops Pty Ltd (No 8). In that case, Cadbury sought to in effect trademark the colour purple by alleging that Darrel Lea chocolates use of a similar shade constituted misleading or deceptive conduct under consumer law. To that end marketing experts were obtained to comment on misinference, misassociation and misidentification practices. The Federal Court, in finding that there was no misleading conduct, held that market research is rarely likely to assist resolving a dispute nor was an expert’s interpretation of consumer behaviour useful. Furthermore, the court was critical of the experts who lacked experience in the ‘retail confectionary market’.
Accordingly, it is wise to comprehensively prepare expert reports and make sure a logical reasoning process is evident from the reports. In addition, the reports or any evidence given should be served on the other side with appropriate promptness and any matters should be within the expert’s area of expertise.
 S79(1) Evidence Act 1995 (NSW)
  NSWSC 930
  NSWSC 411
 (2011) 277 ALR 61
 S135(c) Evidence Act
  NSWCA 56
 S55 Evidence Act
  FCA 470