Expert Opinion or Common Knowledge?

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Many ideas and facts taken for granted as accepted, common knowledge were once in the realm of expert knowledge. For example, at certain points in history, there has been an argument over whether the earth is round, whether smoking causes cancer, whether the continents have drifted over time, whether germs cause disease, and whether the earth is part of a larger solar system and not an isolated environment. Though in the past the truthfulness of these issues was contested and argued, today they are all taken for granted as accepted truths.

Without a doubt, much of the expert opinion adduced in Australian courtrooms will one day be deemed common knowledge, and an expert will no longer be required to provide testimony on the issue. Decision makers must consider when a fact becomes such common knowledge that it no longer requires an expert witness to testify as to its fundamental truthfulness. In this blog, we explore how Australian courts have approached the issue of determining whether evidence is worthy of an expert opinion. We also look into various US case studies surrounding the issue of common knowledge versus expert evidence.

Dasreef Requirements

The High Court’s judgement in Dasreef Pty Ltd v Hawchar[1] sets out the elements which must be demonstrated in order to render expert opinion admissible under s79 of the Evidence Act 1995 (NSW) (NSW Evidence Act). Section 79 of the NSW Evidence Act provides that a person who has “specialised knowledge based on the person’s training, study or experience” is not subject to the opinion rule[2] if the evidence they are providing is “wholly or substantially based on that knowledge”.

The High Court held that the following three elements must be met in order for expert evidence to be admissible under the NSW Evidence Act:

  1. The opinion evidence must concern a topic that is expert in nature;
  2. The expert witness must have “’specialised knowledge based on the person’s training, study or experience” which is specific to the opinion handed down in the trial; and
  3. The opinion provided must be “wholly or substantially based on that knowledge”.

The High Court repeated the comments made by the NSW Court of Appeal in Makita v Sprowles[3]:

“the expert’s evidence must explain how the field of ‘specialised knowledge’ in which the witness is expert by reason of ‘training, study or experience’, and on which the opinion is ‘wholly or substantially based’, applies to the facts assumed or observed so as to produce the opinion propounded”

In Honeysett v The Queen[4] (Honeysett) the High Court specifically addressed the issue of distinguishing “common knowledge” from “specialised knowledge” noting that:

“Specialised knowledge” is to be distinguished from matters of “common knowledge”. Specialised knowledge is knowledge which is outside that of persons who have not by training, study or experience acquired an understanding of the subject matter. It may be of matters that are not of a scientific or technical kind and a person without any formal qualifications may acquire specialised knowledge by experience. However, the person’s training, study or experience must result in the acquisition of knowledge.”

The US Approach

US Courts have also considered the issue of the thresholds which must be met in order for expert evidence to be admissible. The leading case on this issue is Daubert v Merrell Dow Pharmaceuticals[5], from which the High Court of Australia took guidance in their Honeysett decision. Daubert set out the following guidelines for determining the admissibility of expert evidence:

  • The judge is the “gatekeeper” of expert evidence and must assure that expert evidence proceeds from “scientific knowledge”. The burden rests on the proponent of the evidence to demonstrate that the evidence is a product of sound scientific methodology in order to qualify as “scientific knowledge”; and
  • The judge must determine that the evidence is relevant and reliable.

The Court also set out factors to consider in determining the validity of scientific testimony, for example, the degree to which the technique or theories are accepted by a certain scientific community. The relevant US statute governing this issue was amended following this decision to provide that:


A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:

(a) The expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;

(b) The testimony is based on sufficient facts or data;

(c) The testimony is the product of reliable principles and methods; and

(d) The expert has reliably applied the principles and methods to the facts of the case.

This issue is currently being litigated in the US, with a plaintiff claiming that a judge abused her discretion by undertaking a Daubert analysis. In this case, the plaintiff contends that since the medical community generally recognises the fact trying to be proven (this being that zinc in a denture glue product could cause neurological injuries) a Daubert-style examination was unnecessary since the causal links between the product and the conditions were so well established.

A conclusion that expert evidence is not required to prove a certain fact once that fact has been accepted by a court is not beyond the realms of US Courts. The Florida Supreme Court has previously reached the conclusion that tobacco causes lung cancer. As a result, plaintiffs do not need to bring expert testimony to prove this fact. Rather, they simply need to show that their case of lung cancer was not caused by a factor other than tobacco.

In previous US cases, courts have rejected expert evidence on the basis that the testimony described matters of common knowledge. For example, the evidence of a police officer as to the safe driving speed at a crash site based on the conditions at the time of the accident[6], or evidence given on whether an advertisement suggested a preference for one religious group over another[7].


It appears clear that Australian courts will, over time, be required to determine whether evolving educational standards and scientific developments warrant the conclusion that evidence formerly in the domain of expert evidence has moved into the realm of common knowledge. Dasreef and Honeysett set out strong judicial guidelines that aid Australian courts in determining whether such evidence should be admitted under the expert opinion exception to the expert witness rule.

[1] 243 CLR 588

[2] Section 76 of the NSW Evidence Act provides that evidence of an opinion is not admissible to prove the existence of a fact about the existence of which the opinion was expressed. For example, the testimony “Natalie was sad” may not be used to prove that Natalie was, in fact, sad but may be admitted to show that the witness held the state of mind that Natalie was sad.

[3] [2001] NSWCA 305

[4] (2014) 253 CLR 122

[5] 509 U.S 579 (1993)

[6] Coppola v Commonwealth, 220 Va. 243 (1979)

[7] Commonwealth v Lotz Realty Co., 237 Va. 1 (1989)

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