Introduction
The High Court’s decision in Dasreef Pty Ltd v Hawchar [2011] HCA 21 has been significant as the threshold requirements for the admissibility of expert evidence are clarified (French 2012). This essay will first discuss the facts of the case, followed by the technical requirements and perceived difficulties related to expert evidence identified by the court in this case.
Facts
Mr Hawchar, the respondent claimed damages from his employer, Dasreef Pty Ltd, the appellant as he was diagnosed with silicosis allegedly caused by the unsafe working environment. An expert, Dr Basden was retained to provide a report centering on the foreseeability of the alleged injury claimed by Mr Hawchar and procedures that Dasreef could take in reducing the risk of injury.
The case originated in the Dust Diseases Tribunal where the judge relied on the estimate of the expert evidence in calculating the levels of silica Mr Hawchar was exposed to. This led to a finding that the level of exposure exceeded the applicable standard and was appealed by Dasreef before the Court of Appeal as to the admissibility of the expert’s report. The Court of Appeal dismissed the appeal on the basis that the estimate provided in the report was drawn from the expert’s experience, and thus admissible. The admissibility issue of the expert evidence was then brought to the High Court before the judges, French CJ, Gummow, Hayne, Crennan, Kiefel and Bell JJ with Justice Heydon dissented from the majority. It should be noted that the majority analysed the admissibility issue under the Evidence Act while Justice Heydon took a different approach by taking into account the common law requirements. The following sections discuss the admissibility requirements identified by the High Court.
Relevance
According to paragraph 31 of the case, the majority stated that the relevance of the expert evidence is important in considering the operation of s79(1) of Evidence Act, which in turn affecting the admissibility of that evidence. In this case, Dr Basden’s opinion was relevant to proving whether or not there were adequate safety measures in the working environment of Dasreef. However, it was used to quantify the numerical exposure in which the estimates provided in the opinion was not based on Dr Basden’s specialized knowledge based on his training, study or experience, as required by s79(1). The majority found that ‘the form of his opinion did not connect the estimate with his relevant specialized knowledge’ and hence not admissible on this basis (Dasreef Pty Ltd v Hawchar [2011] HCA 21 at paragraph 34).
Criteria governing s79(1) of Evidence Act
The majority also identified two criteria that must be satisfied under s79(1) for the evidence to be admissible, these include: i. The expert has specialized knowledge based on his or her training, study or experience. ii. The opinion evidence is wholly or substantially based on that knowledge.
The first criterion was addressed in paragraph 37 of the case. By referring to the judgment in Makita (Australia) Pty Ltd v Sprowles [2001] NSWCA 305, in order for the opinion to be admissible, there must be an explanation as to ‘how the relevant field of specialized knowledge applies to the assumed or observed facts to produce the expert’s opinion’ (Dasreef Pty Ltd v Hawchar [2011] HCA 21 at paragraph 37). The second criterion is related to the relevance requirement mentioned earlier, where it is necessary for the expert to demonstrate the connection between his or her expertise and the opinion provided. In other words, the opinion needs to be presented in a way that can explain that it is based on training, study or experience (Dasreef Pty Ltd v Hawchar [2011] HCA 21 at paragraph 36).
The common law requirements
Justice Heydon identified three common law requirements in relation to the admissibility of expert evidence in this case, these include: i. The facts and assumptions which the opinion is based must be identified (Dasreef Pty Ltd v Hawchar [2011] HCA 21 at paragraph 64). ii. The facts and assumptions identified must be proved with admissible evidence (Dasreef Pty Ltd v Hawchar [2011] HCA 21 at paragraph 66). iii. The reasoning process applied by the expert in reaching the conclusion which flows from the facts or assumptions identified and proved (Dasreef Pty Ltd v Hawchar [2011] HCA 21 at paragraph 91).
The first and third requirements are retained by the text of s79(1) discussed above. In other words, in order to satisfy s79(1), it is necessary for the expert to identify the facts and assumptions of the opinion and also the reasoning process in reaching the conclusion. However, as with majority’s comment in paragraph 37, it should be noted that the lack of reasoning process is a matter of weight and not admissibility. The second requirement, which is also known as basis rule, remains controversial in determining the admissibility of the evidence.
Perceived difficulties related to expert evidence
The perceived difficulties with expert opinion evidence were identified in the case by Justice Heydon. Firstly, there is a perceived partiality of expert witnesses in some cases. In the example given by his honours in paragraph 56, the experts often become advocate to their clients and give contradictory views in different cases. Secondly, due to the large volume of expert evidence in some cases, the efficiency of the proceedings is affected and more costs are incurred. This can be related to the basis rule supported by Justice Heydon which requires the proof of facts and assumptions based on admissible evidence. The opponent of this rule argued that it is a ‘costly and time consuming procedure which would interrupt the smooth running of trials’ (Dasreef Pty Ltd v Hawchar [2011] HCA 21 at paragraph 117). Thirdly, there is a tendency where there is excessive influence of expert on the trial process. This is a result of information asymmetry as the experts possess more knowledge in a particular field than the judges do, which in turn have a significant impact over the outcome. There are also cases where experts do not conform to the rules of evidence and drift into convincing the courts to accept their evidence (Dasreef Pty Ltd v Hawchar [2011] HCA 21 at paragraph 58).
Conclusion
In short, the admissibility requirements drawn from this case can be summarized as follow: i. The specialized knowledge should be clearly stated and relevant to the opinion provided. ii. Detailed reasoning process is necessary to shat the opinion is wholly or substantially based on the specialized knowledge (Murphy 2011).
However, as stated earlier, the basis rule is not being considered by the majority in this case and hence remains as a question whether the proof of the factual assumptions is required.