Evidence Act 1995, Pt 3.3 (ss 76–80)

[4-0600] The opinion rule — s 76

The opinion rule is stated in s 76. Evidence of an opinion is not admissible to prove the existence of a fact about the existence of which the opinion was expressed. The starting point in determining the admissibility of evidence of opinion is relevance: the opinion rule is expressed as it is to direct attention to why the party tendering the evidence says it is relevant. Particularly, it directs attention to the finding which the tendering party will ask the tribunal of fact to make: Dasreef Pty Ltd v Hawchar (2011) 243 CLR 588 at [31].

The specific exceptions to the opinion rule are listed in the Note to the text of s 76, and include lay opinion (s 78), Aboriginal and Torres Strait Islander traditional laws and customs (s 78A), expert opinion (s 79) and admissions (s 81).

The term “opinion” is not defined in the statute. In the context of the general law of evidence, “opinion” has been defined as “an inference from observed and communicable data”; the text writers accepting that definition are identified by Lindgren J, and the definition is applied to the Evidence Act, in Allstate Life Insurance Co v ANZ Banking Group Ltd (No 5) (1996) 136 ALR 627 at 629. This decision has been accepted as correct by the Full Federal Court, in Bank of Valletta PLC v National Crime Authority (1999) 165 ALR 60 at [20], when upholding (at [22]) a ruling that a statement that the NCA had not obtained “any further information which identifies any relevant offence or any suspect” was a statement of negative fact and not an inference from observed and communicable data. The definition has now been accepted by the NSW Court of Appeal as applicable to the Evidence Act, in Seltsam Pty Ltd v McNeill [2006] NSWCA 158 at [118]–[122]. The many difficulties in the application of such a test are discussed, but not resolved, in R v Smith (1999) 47 NSWLR 419 at [15] et seq. The High Court has, however, referred to the definition of an opinion as “an inference from observed and communicable data” as sufficient for its purpose in Lithgow City Council v Jackson (2011) 244 CLR 352 at [10].

It has been held that the state of a person’s mind is a fact and remains a fact whether what is under discussion is an actual state of mind, or the state in which a person’s mind would be in some contingency which has not happened, and thus it does not fall within s 76: Seltsam Pty Ltd v McNeill, above, at [123].

Recognition evidence: In R v Smith, above, Sheller JA said (at [22]), with the concurrence of the other two judges of the Court of Criminal Appeal, that an identification of a person from a photograph by another person who knows the first person well enough to recognise that person on sight involves no more inference than seeing that person and recognising him in the street. In R v Leung (1999) 47 NSWLR 405, Simpson J, in the course of dealing with the admissibility of the evidence of an ad hoc expert on voice recognition (see s 79), made the same point (at [43]), with the concurrence of the other two members of the court, when discussing the line to be drawn between opinion evidence and evidence of fact.

R v Smith was reversed in the High Court on the ground that the evidence of recognition from a photograph, given by two police officers who were not witnesses to the crime, could not rationally affect the jury’s assessment of the issue, and was therefore irrelevant, as they were in no better position than the jury to determine the issue: Smith v The Queen (2001) 206 CLR 650 at [10]–[12]. However, the majority of the court did (at [9], [11], [14]–[15]) leave open the possibility that such recognition may be relevant where there was some distinctive feature concerning the person depicted known to the police officers that would not be apparent to the jury. See, for example, R v Robinson [2007] QCA 99 at [20]. Kirby J, who dissented on the issue of relevance in Smith v The Queen, above, accepted (at [54]) the statement made by Sheller JA, but said (at [57]–[58]) that the dangers of mistakes inherent in the processes of identification and recognition make it unsurprising that evidence such as that given by the police officers has normally been classified as opinion rather than factual evidence. It has since been held, following the views of Kirby J, that, where the recognition evidence becomes relevant and thus admissible in accordance with the majority judgment, but where the photographs are of poor quality, or provide only an unusual angle or obscure part of the person in question, it is more appropriate to classify evidence of recognition as opinion evidence rather than evidence of fact: R v Drollett [2005] NSWCCA 356 at [41]–[44].

Where there has been no process of deduction rather than recognition, and no real risk of the recognition being wrong — because, for example, the familiarity the witness has with the person in question — it may still be appropriate to accept the evidence of recognition as evidence of fact rather than opinion: R v Marsh [2005] NSWCCA 331 at [18], [31]; R v Drollett, above, at [60]. See also Nguyen v R (2007) 180 A Crim R 267, discussed under s 78 (Exception: lay opinions).

In Haidari v R [2015] NSWCCA 126, Johnson J (with whom the other members of the court agreed) considered an identification issue in a trial concerning a detention centre riot. The issue was whether a client service officer at the Villawood Detention Centre had permissibly identified the appellant as a person taking part in the riot. The officer without objection purported to identify the appellant from his own observations and in an ABC film clip taken on the night. He knew the appellant from his professional dealings with him. Johnson J rejected the argument that the identification was opinion evidence. His Honour, at [76], distinguished R v Drollett, making the important point that there is no bright line between opinion and fact. He described it as “a blurred boundary”, to be determined by a close examination of the circumstances in each case. The court held that there had been no miscarriage of justice: at [78].

Hearsay evidence of opinion: The admissibility of hearsay evidence of an opinion which falls within an exception to the hearsay rule is still governed by Pt 3.3 (ss 76–80) of the Evidence Act: R v Whyte [2006] NSWCCA 75 at [36], [51]. The evidence in that case was of the complainant (in a prosecution of the appellant for detaining her with intent to have sexual intercourse with her) that she had told her mother that the accused had tried to rape her. It was admissible on the issues of credit and absence of consent, and as opinion evidence pursuant to s 78 (lay opinion). It should be noted that the two judges who dealt with this issue did not agree as to the basis for its admissibility under Pt 3.3, but they were agreed that Pt 3.3 applied. The decision does not appear to have been the subject of further judicial examination.

[4-0610] Exception: evidence relevant otherwise as opinion evidence — s 77

The Reports of the Australian Law Reform Commission did not discuss this provision. It is suggested by S Odgers, Uniform Evidence Law (13th edn) at [EA.77.60], that the intention of s 77 is the same as that of s 60 — to overcome the unrealistic distinctions the common law drew in relation to hearsay evidence. Odgers analyses the facts of R v Whyte, above, to suggest that s 77 could have been applied in that case — the evidence was sought to be used, not to prove (in the words of s 77) “the existence of a fact [the appellant intended to have sexual intercourse with her] about the existence of which the opinion was expressed”, but to establish her credibility, so that s 77 excludes the opinion rule, and the evidence therefore becomes evidence of the truth of that fact.

Only minimal judicial exegesis of this section can be found. In most of the cases where s 77 was raised, the evidence was held to be factual rather than opinion evidence, and the proper interpretation of the provision was not attempted.

In ACCC v Real Estate Institute of Western Australia Inc [1999] FCA 675, the ACCC alleged contravention of prohibitions imposed and regulation by the Trade Practices Act 1974 of certain franchise agreements and rules governing solicitation and advertising (described at [2]). Evidence was to be given by witnesses in which general observations were made about the markets in which they operated and the competitive processes in those markets (described at [6]). The evidence of such perceptions and practices was put forward by the ACCC as relevant even if based on hearsay or opinion, not because it established the truth of the facts perceived but because it was to establish the perception of experienced market participants whose competitive decisions are driven by such perceptions (see [6]). The evidence was objected to on the basis that it consisted of statements of opinion and of conclusion and opinion, and that it was at too high a level of generalisation (see [8]). French J held (at [10]) that, to the extent the evidence was relied on as evidence of perception or as explanatory of the behaviour of industry participants, it appeared to attract the operation of s 77, and that the circumstance that such opinion was based on observations expressed compendiously but not specifically analysed went to the weight and not the admissibility of that evidence. This decision does not appear to have been the subject of any other judicial consideration.

[4-0620] Exception: lay opinions — s 78

The common law recognised that lay opinion evidence would be admissible where the basis of a witness’s impression was either too evanescent or too complicated to be separately and distinctly narrated, because the witness was better equipped than the jury to form an opinion on the matter: Heydon, Cross on Evidence at [29085], relying on Wigmore, 3rd edn, 1918. The author of Cross on Evidence, at [29090], has identified the following typical instances of admissible non-expert opinion — age, sobriety, speed, time, distance, weather, handwriting, identity, bodily health, emotional state, the physical condition of things, the reputation and character of persons, impressions of a person’s temperament, relationships and attitudes. The identification of a person known to the witness from a photograph is, however, factual and not opinion evidence: R v Leung (1999) 47 NSWLR 405 at [43], see [4-0600] above.

In proposing what is now s 78, the Australian Law Reform Commission considered whether there should be an express requirement that the opinion be rationally based, but did not propose such a requirement because it contemplated that such a provision would be so interpreted or, if it were not, the second requirement — that the evidence is necessary to obtain an adequate account or understanding of the person’s perception of the matter or event — should provide sufficient protection: ALRC Report 26, vol 1, pars 739–740. The Court of Criminal Appeal has interpreted s 78 as so contemplated: R v Panetta (1997) 26 MVR 332 at 332; as has the Federal Court, in Guide Dog Owners’ and Friends’ Association Inc v Guide Dog Association of New South Wales and ACT (1998) 154 ALR 527 at 531 (proposition (3)).

A witness’s perception of the matter or event will typically be formed and expressed either as opinion or as a mixture of fact and opinion; the Australian Law Reform Commission recognised (at pars 350–351 and 349 of ALRC Report 26, vol 1) that witnesses cannot aspire to a perfect and non-modified reproduction of the data perceived, and that the opinion may be the only evidence of the perception: Connex Group Australia Pty Ltd v Butt [2004] NSWSC 379 at [24]–[26]. Where a plaintiff claims damages for injuries suffered arising out of the defendant’s defective premises, a question effectively asking whether he or she would nevertheless still have been injured even if the defendant’s premises had not been defective, thus involving retrospective reasoning on the plaintiff’s part, is nevertheless relevant: Ellis v Wallsend District Hospital (1989) 17 NSWLR 553 at 560, as applied in Taber v NSW Land and Housing Corporation [2001] NSWCA 182 at [69] et seq.

However, the absence of a factual basis for a characterisation given by a witness to an event which goes to the heart of the issue in the case may affect the weight to be given to the characterisation, justifying its rejection pursuant to s 135 and s 137 as unfairly prejudicial: R v Harvey (unrep, 11/12/1996, NSWCCA) at 6–7; R v Van Dyk [2000] NSWCCA 67 at [133]–[134]; Guide Dog Owners’ and Friends’ Association Inc v Guide Dog Association of New South Wales and ACT at 532.

In Nguyen v R (2007) 180 A Crim R 267, the four accused were identified by two police officers, who had known them for some time, as the four men shown in a CCTV record (and in still photographs extracted from the CCTV record) preparing to commit the crimes charged — the murder of one person and the malicious infliction of grievous bodily harm of another person with intent to do so. The basis on which the identification relied consisted of the police officers’ previous detailed knowledge of the activities of the accused (which were established in evidence) and what they perceived from the CCTV record, and thus went beyond the material otherwise available to the jury (at [23]–[25]). The circumstance that the police officers’ opinion was based on more than the material already available to the jury established that their opinion could rationally affect the jury’s assessment of the facts in accordance with s 55 (Relevant evidence): Smith v The Queen (2001) 206 CLR 650 at [10]–[11]. The descriptions of the accused given by the police officers was evidence of fact, but the identification of the men made by the two offers was evidence of opinion: Nguyen v R at [30], see also [59].

Section 78 assumes that the matter or event as perceived by the witness is relevant to the proceedings: R v Leung, above, at [28]–[33].

Emphasis has been placed on the requirement of s 78(b) that, not only must the opinion be based on what the witness saw, heard or otherwise perceived but that evidence of that opinion must also be necessary to obtain an adequate account or understanding of the witness’s perception of the matter or event: Partington v R (2009) 197 A Crim R 380 at [37]–[46]. In that case, in which the Crown alleged that the accused had killed the deceased by damage he caused to his spinal cord, a witness, who was standing inside the front door of an apartment outside which the accused and the deceased were together, gave evidence that she heard bangs against the door and she expressed the opinion that “somebody’s head was being pushed up against the door”. It was held, by majority, at [47], that she had not relevantly perceived the particular event that was alleged to have caused death and that her belief as to what was causing the noises she heard was not necessary to understand her evidence of that perception.

An opinion expressed by ambulance officers who had not seen the plaintiff fall as to how he had fallen, based upon inferences they had drawn from the physical circumstances of the area in which he had fallen, does not qualify as an asserted fact within the meaning of s 76 (the opinion rule): Lithgow City Council v Jackson (2011) 244 CLR 352 at [17], [77], [83].

See Honeysett v The Queen (2014) 253 CLR 122, for the situation where an expert opinion (wrongly admitted) does not qualify, in the circumstances, as a lay opinion.

[4-0625] Exception: Aboriginal and Torres Strait Islander traditional laws and customs — s 78A

The Explanatory Memorandum for the Evidence Amendment Act accepted the recommendation of the ALRC Report 102 that a member of an Aboriginal or Torres Strait Islander Group should not have to prove that he or she has specialised knowledge based on training, study or experience before being able to give opinion evidence about the traditional law or custom of his or her own group. See Re: Estate Jerrard, Deceased (2018) 97 NSWLR 1106 at [69]–[79], [95]–[96]. See further, generally, [4-0420] dealing with a similar provision relating to hearsay evidence.

[4-0630] Exception: opinions based on specialised knowledge — s 79(1)

Last reviewed: March 2024

Section 79(1) has two conditions of admissibility: first, the witness must have “specialised knowledge based on the person’s training, study or experience” and, secondly, the opinion must be “wholly or substantially based on that knowledge”. In Honeysett v The Queen (2014) 253 CLR 122, the High Court explained at [23]–[24] that the “first condition directs attention to the existence of an area of specialised knowledge. 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 Macquarie Dictionary defines ‘knowledge’ as ‘acquaintance with facts, truths, or principles, as from study or investigation’ (emphasis added) and it is in this sense that it is used in s 79(1). The concept is captured in Blackmun J's formulation in Daubert v Merrell Dow Pharmaceuticals Inc (1993) 509 US 579 at 590: ‘the word “knowledge” connotes more than subjective belief or unsupported speculation. ... [It] applies to anybody of known facts or to any body of ideas inferred from such facts or accepted as truths on good grounds”.

The second condition of admissibility under s 79(1) allows that it will sometimes be difficult to separate from the body of specialised knowledge on which the expert’s opinion depends “observations and knowledge of everyday affairs and events”. It is sufficient that the opinion is substantially based on specialised knowledge based on training, study or experience. It must be presented in a way that makes it possible for a court to determine that it is so based: Honeysett v The Queen, above, at [24].

The opinion is admissible even if proof of the factual basis for that opinion is controversial and the issues relating to the factual basis cannot be resolved until the end of the trial; the opinion evidence is admissible if there is evidence which, if accepted, is capable of establishing the truth of the assumptions: Rhoden v Wingate [2002] NSWCA 165 at [86].

Basis of admissibility: The High Court clarified in Dasreef Pty Ltd v Hawchar (2011) 243 CLR 588 at [37]) that the admissibility of opinion evidence is to be determined by the application of the requirements of the Evidence Act rather than by the application of statements made in decided cases divorced from the context in which those statements were made. The joint majority judgment has nevertheless adopted Heydon JA’s statement in Makita (Australia) Pty Ltd v Sprowles (2001) 52 NSWLR 705 (at [85]), that 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 in the particular case so as to produce the opinion propounded. Note, the principles stated in Makita v Sprowles and applied in Dasreef Pty Ltd v Hawchar regarding the admissibility of expert opinion evidence under the uniform evidence legislation, apply equally to the determination of admissibility at common law: Lang v The Queen [2023] HCA 29 at [11]; [430]–[434].

No expert evidence is based exclusively on the expert's training, study, or experience. All fields of specialised knowledge assume “observations and knowledge of everyday affairs and events, and departures from them”, it being the “added ingredient of specialised knowledge to the expert’s body of general knowledge that equips the expert to give [their] opinion”: Lang v The Queen at [435]; Kiefel CJ and Gageler J at [12]; Velevski v The Queen [2002] HCA 4 at [158].

While expert opinion evidence must have a rational relationship with the facts proved (or anticipated to be proved) to be admissible, the requirement is for purported, not actual, justification for the opinion expressed: Lang v The Queen at [436].

The analysis in Dasreef accepts (at [41]) that the Evidence Act does not require the factual basis of the opinion to be established: see “Differentiation between opinion and factual basis; identification of factual basis” (below).

It is accepted that an expert need not amass all of the factual data on which the opinion is to be expressed; the task can be delegated to another, but it is necessary for the expert who is the author of the report to apply his or her mind to the analysis and reasoning that any subordinates have developed, so that, when the report is finalised, the whole of the reasoning and conclusions it contains have been adopted as the expert’s own reasoning and conclusions: ASIC v Rich (2005) 190 FLR 242 at [329]; R v Jung [2006] NSWSC 658 at [57], where Hall J gives the example of an MRI produced by a radiologist which is then utilised by a medical specialist for the purposes of forming an opinion concerning causation, diagnosis or treatment. See also Paino v Paino (2008) 40 Fam LR 96 at [66]–[67], [113].

The decision by the trial judge as to whether the opinion was wholly or substantially based on the expert’s knowledge is to be determined on the balance of probabilities (s 142), and — in accordance with the principle in Blatch v Archer (1774) 98 ER 969 at 970; Weissensteiner v The Queen (1993) 178 CLR 217 at 225–228 and Ho v Powell (2001) 51 NSWLR 572 at [14]–[15] — the evidence is to be weighed according to the proof which was in the power of one side to have produced, and in the power of the other to have contradicted: Paino v Paino at [72]–[74]. In Gilham v R (2012) 224 A Crim R 22, the trial judge had been confronted with evidence from two forensic experts opining in relation to the “similarity” of the pattern of stab wounds on the victims. The evidence was permitted and the Crown allowed to address the jury to suggest the “extraordinary co-incidence” of the similarity pointed to one perpetrator causing the death of all three victims. Applying the Dasreef test, the Court of Criminal Appeal held, at [345], that the absence of any evidence of relevant experience of fatal stab wounds inflicted by the one killer on multiple victims meant that the evidence of the experts should not have been admitted. Second, its prejudicial impact was such that it ought, in any event, to have been rejected under s 137 of the Evidence Act. In addition, the court was critical of the decision by the Crown (at the first trial) not to call an expert forensic witness the Crown had engaged whose opinion differed markedly from the other two experts. The court, at [412], stated that the Crown’s failure to call the witness at the second trial constituted a miscarriage of justice.

“specialised knowledge”: The “specialised knowledge” test was preferred by the Australian Law Reform Commission to the “field of expertise” test — enunciated in Frye v United States 293 F 1013 (1923), followed in R v Gilmore [1977] 2 NSWLR 935 at 939–941, and continued, despite its reversal in the United States, in R v Pantoja (1996) 88 A Crim R 554 at 558 — because of the difficulties experienced in implementing such a test and the unnecessary restrictions it imposed: ALRC Report 26, vol 1 at 743; ALRC Report 38 at 149–150.

The term “specialised knowledge” is not defined in the Evidence Act. The analogous term “expertise” adopted at common law requires a “peculiar” skill on the part of the witness (that is, one out of the ordinary experience of others); that person’s opinion becomes admissible only where the subject matter of inquiry is such that inexperienced persons are unlikely to prove capable of forming a correct judgment on it without such assistance and it is of such a nature as to require a course of previous habit or study in order to do so: Clark v Ryan (1960) 103 CLR 486 at 491. An alternative formulation of the common law test is that expert opinion evidence is admissible where the information it conveys is likely to be outside the experience and knowledge of a judge or jury: Murphy v The Queen (1989) 167 CLR 94 at 111, 126, 130; Thirukkumar v Minister for Immigration and Multicultural Affairs [2002] FCAFC 268 at [18], [33]–[34]; Forbes v Selleys Pty Ltd [2004] NSWCA 149 at [56].

The phrase “specialised knowledge” in s 79 was intended to extend the common law, and to emphasise that experience can be a sounder basis for opinion than study: ALRC Report 26, vol 1, par 742. The phrase is “not restrictive; its scope is informed by the available bases of training, study and experience”: Adler v ASIC (2003) 46 ACSR 504 at [629], in which it was held that proper professional conduct, in the sense of due care and obedience to customary practices and ethical rule, was a field of specialised knowledge.

Honeysett v The Queen (2014) 253 CLR 122 is an important contribution to the learning on “opinion evidence”. It represents a necessary caution against allowing expert opinion where it is based essentially on a subjective appreciation of facts which may be equivalently assessed by the tribunal of fact.

The appellant was convicted of the armed robbery of a suburban hotel. CCTV cameras had captured images of the robbery. Professor Henneburg, an expert in anatomical matters, gave evidence of physical characteristics that were common to both the appellant and one of the robbers. Over objection, the evidence was admitted (and used by the Crown) as an item of circumstantial evidence to support a conclusion of identity.

The High Court held that the opinion expressed by the expert was based on his subjective impression of what he saw when he examined the CCTV images. However, the court said the admission of the evidence gave the “unwarranted appearance of science” to the prosecution case. His opinion was not based “wholly or substantially on his specialised knowledge” within s 79(1) and had been wrongly admitted at the trial. The court also held that, in the circumstances, Professor Henneburg’s opinion was not admissible as that of an “ad hoc” expert. A new trial was ordered.

A practical application of this necessary caution is to be found in the decision of Harrison J in Beckett v State of New South Wales [2014] NSWSC 1112.

At issue was an expert report sought to be tendered in proceedings brought by the plaintiff seeking damages for malicious prosecution. In essence, the report sought to analyse in detail the behaviour of the former detective who had been the prosecutor in the criminal proceedings giving rise to the malicious prosecution. The conduct in question involved (so it was said) intimidating witnesses; causing witnesses to give false testimony; bias and fabricating or planting physical evidence to inculcate Ms Beckett in the criminal charge of attempting to murder her husband. The expert report in question was that of a former policeman who sought to bring to bear his experience and knowledge gained over many years on the propriety of the prosecutor’s actions in assembling evidence against Ms Beckett in the criminal proceedings.

Harrison J found that (with one exception) none of the matters in the report fell within the reach of any identifiable expertise. Nor was the expert opinion on these matters otherwise relevant in the malicious prosecution proceedings. Importantly he held (echoing Honeysett) that the expert’s opinions were necessarily subjective opinions, divorced from any independent means of validation. They were not amenable to “measurement and calculation” and therefore inadmissible.

Recently, the same point was made in Verryt v Schoupp [2015] NSWCA 128. The respondent was a 12-year-old boy who had been badly injured while being “towed” on a skateboard behind a motor vehicle. The principal issue on appeal was one of contributory negligence. However, a subsidiary issue related to the admissibility of a “psychiatric report” which purported to express opinions as to how a 12-year-old boy was likely to have acted and thought in the circumstances of the accident. The psychiatrist had not made any psychiatric assessment of the respondent. Meagher JA at [59] (with whom the other members of the court agreed) held that the psychiatrist’s evidence was not based on any specialised knowledge of a 12-year-old child’s behaviour in the circumstances of the accident. For that reason, it was not admissible under s 79.

See also, Howard Smith and Patrick Travel Pty Ltd v Comcare [2014] NSWCA 215. This case dealt with the admissibility of an opinion expressed by stevedoring workers that they had been exposed to asbestos dust during their employment. The evidence was allowed as evidence by lay witnesses as to their perception. It also qualified as admissible evidence on the basis that it was specialised knowledge obtained through extensive experience.

In BHP Billiton Ltd v Dunning [2015] NSWCA 55, the Court of Appeal upheld the admissibility of the evidence of a non-expert witness that material in a steelworks factory was or contained asbestos. The witness was well familiar with the operations of the steelworks and was the person responsible for testing replacement materials for asbestos and their efficacy. The court held that the evidence was admissible as “objectively observed fact”: at [101].

In some cases, the link between the opinion expressed by the witness and his or her training, study or experience will be apparent from the nature of the specialised knowledge, such as an opinion on general conveyancing practice expressed by a solicitor with specialised knowledge of that practice, but the link would not be apparent in relation to an exotic matter of conveyancing practice, and in such a case it would have to be spelt out: Adler v ASIC, above, at [632].

The expert’s reasoning process should be sufficiently exposed to enable an evaluation as to how the expert used his or her expertise in reaching the opinion stated: HG v The Queen (1999) 197 CLR 414 at [39]–[41]; Makita (Australia) Pty Ltd v Sprowles at [85]; Keller v R [2006] NSWCCA 204 at [28]–[31]; Rylands v R (2008) 184 A Crim R 534 at [84].

In Allianz Australia Ltd v Sim [2012] NSWCA 68 the Court of Appeal held that the evidence of a distinguished pathologist, Professor Henderson, as to the causal link between exposure to asbestos dust and lung cancer was admissible. The opinions expressed emerged wholly or substantially from his expertise and knowledge so as to comply with s 79. Further, the expert was entitled to express an opinion about the ultimate causation issue: s 80.

Opinions based on the expert witness’s own interpretation of the evidence are not inadmissible, provided that the reasoning process is properly explained and is shown to depend on the expert’s specialised knowledge: ASIC v Rich (2005) 53 ACSR 110 at [289]–[291].

Where the provisions of the Evidence Act apply, the judge is permitted to take into account only those facts proved in evidence or matters of which judicial notice could be taken; matters of which the judge is otherwise aware from experience in a particular area are not relevant: Dasreef Pty Ltd v Hawchar (2011) 243 CLR 588 at [47], overruling a long line of authority in the Full Court and the Court of Appeal starting with Bryce v Metropolitan Water Sewerage and Drainage Board (1939) 39 SR 321 at 330.

Bartlett v ANZ Banking Group Ltd (2016) 92 NSWLR 639; [2016] NSWCA 30 is a reminder that seldom, if ever, will a dispute between experts be resolved by an examination of the witnesses’ demeanour. This will be so unless the witness “has given dishonest or misleading evidence, or has become an advocate for a party, or where the evidence given is inherently unreliable”. The court described observations of an expert’s demeanour as “a last resort”. The differences between experts should usually be resolved by rational analysis.

“based on the person’s training, study or experience”: The words “training, study or experience” necessarily include observations and knowledge of everyday affairs and events and of departures from them, and it will frequently be impossible to divorce entirely those observations and that knowledge from the body of purely specialised knowledge on which an expert’s opinion depends; it is the added ingredient of specialised knowledge to the expert’s body of general knowledge that equips the expert to give his or her opinion: Velevski v The Queen (2002) 76 ALJR 402 at [158]. Reference was also made at [158] to s 80, see [4-0640].

In an appeal from a ruling rejecting expert evidence tendered as to what led members of the public to decide to purchase a particular brand of chocolate because that was quintessentially a question of fact within the experience and knowledge of the tribunal of fact, the Full Federal Court has held that, because of s 80 (Ultimate issue rule abolished), expert evidence remains admissible notwithstanding that the issue to be determined remained within the experience and knowledge of the tribunal of fact: Cadbury Schweppes Pty Ltd v Darrell Lea Chocolate Shops Pty Ltd, above, at [51]–[57]. Special leave to appeal was refused by the High Court, but it appears to have been sought only in relation to the order made by the Full Court that the matter be returned to the original trial judge for further hearing, rather than a new trial before a different judge: Cadbury Schweppes Pty Ltd v Darrell Lea Chocolate Shops Pty Ltd [2007] HCA Trans 468. See also Chen v R [2018] NSWCCA 106 where these matters are reinforced.

In consumer decision-making and similar cases, knowledge of actual mistake or confusion arising where there has been a particularly close similarity in brand names does not amount to specialised knowledge of the factors that may be causative of, and conditions that create the likelihood of, mistake or confusion in the decision-making purchasers that satisfies the test in Clark v Ryan, above: CA Henschke and Co v Rosemount Estates Pty Ltd (1999) 47 IPR 63 at [75]–[76]; these rulings were upheld on appeal: CA Henschke and Co v Rosemount Estates Pty Ltd (2000) 52 IPR 42 at [17]–[18].

A person experienced in training programmes for the long-term unemployed is qualified to express an opinion as to the capacity of such a person to carry out particular types of work becoming available through the Commonwealth Employment Service: Hospitality Excellence Pty Ltd v State of NSW [1999] NSWSC 945 at [10]; but such a person is not, without more, qualified to express opinions as to the probability of that person being employed in that work or the financial benefits from such employment: at [11]–[14].

In Hawkesbury Sports Council v Martin [2019] NSWCA 76, the primary judge erred in admitting expert opinion evidence for the respondent as to matters of visual perception and vision science: at [33]. The expert's report did not explain how his opinions, based on “specialised knowledge”, in turn based on his “training, study or experience” and on which the opinion is “wholly or substantially based”, applied to the facts assumed or observed so as to produce the opinion propounded as required by s 79: at [33]; Makita (Australia) Pty Ltd v Sprowles at [85].

Failure to demonstrate that an opinion is based on a witness’s specialised knowledge, based on his or her training, study or experience goes to the admissibility of the evidence, not its weight: Dasreef Pty Ltd v Hawchar (2011) 243 CLR 588 at [42]; Nicholls v Michael Wilson & Partners Ltd [2012] NSWCA 383 at [209].

“expert witness code of conduct”: Both the Supreme Court Act and Rules and the District Court Act adopt the Expert Witness Code of Conduct provided in Sch  7 to the Uniform Civil Procedure Rules 2005. In Chen v R (2018) 97 NSWLR 915, an interpreter whose written statement had been served, and who was later called to give oral evidence, had not made the acknowledgement required by Pt 75 of the UCPR. The trial judge ruled that the witnesses’ failure to be aware of the expert code did not create an absolute bar to admissibility. He suggested that the issue could be dealt with by appropriate directions to the jury. The court agreed with the trial judge’s decision, holding that failure to comply did not result in the mandatory exclusion of the interpreter’s evidence. However, in an appropriate case, the failure may be relevant to a consideration of the issues in ss 135 and 137 of the Evidence Act. See also Wood v R (2012) 84 NSWLR 581.

The Court of Criminal Appeal, in Wood v R, ordered the acquittal of the accused, Gordon Wood. A significant basis of the court’s decision related to its unfavourable view of the principal expert relied on by the Crown to exclude the possibility of the deceased’s suicide. The decision contains the useful statement of the obligations cast upon an expert both by the general law and the Expert Witness Code of Conduct: [719]–[729].

Differentiation between opinion and factual basis; identification of factual basis: An expert whose opinion is tendered should differentiate between the assumed facts on which the opinion is based and the opinion in question, to enable the court to identify the facts the witness has either observed or accepted and to distinguish between them and the witness’s expressions of opinion; s 79 requires that the opinion be presented in a form which makes it possible to determine whether the opinion is wholly or substantially based on specialised knowledge based on training, study or experience, and such form requires or invites a demonstration or examination of the scientific basis of the conclusion: HG v The Queen (1999) 197 CLR 414 at [39], [41]; TCN Channel Nine Pty Ltd v Anning (2002) 54 NSWLR 333 at [144]; ASIC v Rich at [98]–[101], [109]; R v Tang (2006) 65 NSWLR 681 at [147]–[153]; Hamod v Suncorp Metway Insurance Ltd [2006] NSWCA 243 at [37]; Hancock v East Coast Timber Products Pty Ltd (2011) 80 NSWLR 43 at [69].

If those matters are not made explicit in chief, it would normally not be possible for the court to make a judgment as to whether the prerequisites of s 79 have been satisfied and whether the evidence is admissible, and in any event the opinion will be valueless without proof of such factual basis: Cadbury Schweppes Pty Ltd v Darrell Lea Chocolate Shops Pty Ltd (2007) 239 ALR 662 at [107]–[108]; Hancock at [73]–[78]. The prime duty of an expert is to identify the facts and reasoning process which justify the opinion expressed. That is sufficient to enable the tribunal of fact to evaluate the opinion expressed: ASIC v Rich (2005) 218 ALR 764 at [105]. If, however, the material on which the expert opinion is based is not supported by admissible evidence, the opinion may have little or no value, for part of the basis of the opinion is gone: Hancock at [76], citing Ramsay v Watson (1961) 108 CLR 642 at 649.

Experts who venture opinions outside their field of specialised knowledge, which are sometimes no more than their own inferences of fact, may invest those opinions with a spurious appearance of authority, and legitimate processes of fact-finding may be subverted: HG v The Queen, above, at [44]. In that case, the Chief Justice criticised the psychologist’s opinion tendered in that case has having been based on “a combination of speculation, inference, personal and second-hand views as to the credibility of the complainant, and a process of reasoning which went well beyond the field of expertise of a psychologist”, and held that it had not been shown to have been based, either wholly or substantially, on the proposed witness’s specialised knowledge as a psychologist. By directing attention to whether an opinion is wholly or substantially based on specialised knowledge in which the witness is expert by reason of training, study or experience, s 79 will not be satisfied unless the opinion is presented in the form that makes it possible to answer that question: HG v The Queen at [39].

Sackville AJA repeated this point in Nicholls v Michael Wilson & Partners Ltd [2012] NSWCA 383 at [242] and [243]. It was also reinforced in criminal proceedings in Kyluk Pty Ltd v Chief Executive, Office of Environment and Heritage (2013) 298 ALR 532. Indeed, the latter decision at [63]–[69] and [176]–[179] suggests that in a criminal trial, where important facts supporting an expert opinion have not been proved, s 135 will require the discretionary rejection of the evidence, even where the opinion is arguably admissible.

Where an opinion becomes admissible pursuant to s 79, the absence of explanations, discussion and analysis may reduce its probative value to such an extent that that value would be outweighed by its probative effect: Paino v Paino [2005] NSWSC 1336 (Barrett J) at [27]. (This proposition was not disputed in the subsequent successful appeal: Paino v Paino (2008) 40 Fam LR 96).

The expert evidence of a witness must identify what the witness asserts was an adequate basis for his opinion; matters concerning the process by which an opinion was actually formed go the weight, and not the admissibility, of the evidence, and are relevant to the exercise of the discretion given by s 135: ASIC v Rich at [94]. If the proposed evidence identifies the facts asserted to be the basis of the opinion and the process of reasoning by which the opinion was formed, and if the opinion is capable of being based on those facts, the evidence is admissible: at [135]–[136]. The facts do not need to have been proved at the stage the opinion is tendered: at [136]. The issue then for the tribunal of fact is whether the opinion expressed on the facts proved or assumed is correct; in determining this issue, regard must be had, among other things, to the reasoning process (based on those facts) used by the expert: at [136].

The law remains that there is no requirement in the Evidence Act for the admissibility of opinion evidence that the factual basis of the opinion to be established either before that evidence may be given or at all, although the absence of such factual evidence at the time the opinion is tendered may, subject to s 136, lead to it being admitted conditionally, and its absence at the end of a particular case may lower the weight of any opinion based on the assumption that the factual basis exists to the point where its use may be limited pursuant to s 136. On the other hand, a failure to establish that the opinion expressed by an expert is based on the expert’s specialised knowledge based on training, study or experience goes to its admissibility, not its weight: Dasreef Pty Ltd v Hawchar (2011) 243 CLR 588 at [41]–[42]; applied in Hawkesbury Sports Council v Martin [2019] NSWCA 76 at [28].

In Sharma v Insurance Australia Limited t/as NRMA Insurance [2017] NSWCA 55, the appellant had lost his case at first instance because the trial judge did not accept that the appellant had injured his wrists in a fall from a ladder. Part of the evidence tendered at trial consisted of a number of medical certificates prepared for the purpose of explaining to an employer that the appellant would be unable to attend to his usual employment. These recorded the appellant’s claim to the relevant doctors that he had injured his wrists in a fall. The trial judge found that these certificates assumed the correctness of the medical history provided by the appellant but contained no reasoning process to validate any opinion expressed. Applying Makita (Australia) Pty Ltd v Sprowles, above, and Dasreef Pty Ltd v Hawchar, above, the Court of Appeal held that the medical certificates were not admissible. They did not explain the experts’ fields of “specialised knowledge”, nor the facts on which any opinion was based. In each case, the document was “a medical certificate intended for use in an employment rather than a curial context”. For that and other reasons, the appeal was dismissed.

Evidence given by police officers in relation to covertly recorded conversations between person alleged to have been involved in drug transactions — in which the evidence seeks to translate the codes used by the participants in those conversations as referring to the particular drugs and quantities being bargained — requires close attention to the requirements of s 79 and the application of s 135, in that the witnesses who give such evidence frequently base their opinions on information concerning the participants which is not part of their specialised knowledge, such as information concerning the activities of the participants conveyed by other police officers who had participated in the police investigation. This material must be identified and proved before the opinions become admissible. In many cases, the other activities revealed disclose uncharged conduct and raise tendency problems. The relevant authorities are reviewed in Nguyen v R (2007) 173 A Crim R 557 at [36]–[58].

A good example of the issues that may arise is found in Beech-Jones J’s decision in JP v DPP (NSW) [2015] NSWSC 1669. A police fingerprint expert provided a certificate which gave brief details of his methodology and then certified that, in his opinion, the defendant’s fingerprint was identical to a fingerprint found at a break-and-enter crime scene. However, he was cross-examined over several days and during the cross-examination, gave much more detail of his methodology. Justice Beech-Jones accepted that the brief statements in the report of the fingerprint evidence would not have satisfied the requirement that the claimed field of expertise must be shown to have adhered to the facts found (or assumed) to produce the opinion expressed. In the case of expert fingerprint evidence there must be at least some detail of the points of similarity and how those points have been ascertained and identified. It will often be the case with this type of expert evidence that “little explicit articulation or amplification” will be required: at [33]. However, Beech-Jones J held in dismissing the appeal that the expert’s oral evidence “filled the gaps” and secured admissibility for the expert opinion.

Nguyen v R at [60]–[65] demonstrates the importance of the identification of the specialised knowledge on which such an opinion was based. That decision and a number of earlier cases — Keller v R [2006] NSWCCA 204 at [24]–[31] and Chow v R (2007) 172 A Crim R 582 at [50]–[55] — insist that, in the absence of an identification of the contextual matters which led to the opinion that they were references to drugs, an expert in these cases must be restricted to saying that the code words are consistent with references to drugs.

At the stage when the admissibility of an expert opinion is being considered, and where the factual basis of the opinion is established by hearsay evidence, the opinion is admissible, and the hearsay evidence — having been admitted for the purpose of the admissibility of the opinion — becomes evidence of the truth of the hearsay facts stated in accordance with s 60: Bodney v Bennell (2008) 249 ALR 300 at [92]–[93].

Ad hoc experts: Section 79 is sufficiently wide to accommodate the idea of an ad hoc expert witness: R v Leung (1999) 47 NSWLR 405 at [36]–[40]. Examples given are of a tape-recording that was substantially unintelligible to anyone who had not played it repeatedly but is then played repeatedly by a person until that person is able to decipher it, and of a tape recording in a foreign language that can be deciphered only by a person familiar with the language who plays it repeatedly: R v Menzies [1982] 1 NZLR 40 at 49; Butera v DPP (Vic) (1987) 164 CLR 180 at 187–188; Eastman v R (1997) 158 ALR 107 at 201–203; R v Cassar [1999] NSWSC 436 at [6]–[7]. Nguyen v R [2017] NSWCCA 4 is another example of a police officer listening to intercepted calls over a lengthy period of time. The officer’s repeated listening gave his identification evidence the quality of ad hoc expertise, and thus was admissible as expert evidence.

The Victorian Supreme Court of Appeal accepted that a police detective had the training and experience, falling short of formal qualifications, placing him in a position of having knowledge as to the effects on concrete of burning accelerants beyond that of a person lacking that training and experience: Davies v R [2019] VSCA 66 at [177].

In Morgan v R [2016] NSWCCA 25, the appellant had been convicted of a series of “break and enter” offences by circumstantial evidence and voice identification evidence. A tracking device containing a listening device had been placed in a stolen BMW allegedly used by the appellant and his co-defendants. After a voir dire, the trial judge allowed into evidence the “ad hoc” expert evidence of a police officer in relation to voice similarity. The officer had extensively compared the voices on the listening devices with conversations recorded between the appellant and his partner while he was in custody. The CCA held that Honeysett v The Queen (2014) 253 CLR 122 did not cast doubt on the use of “ad hoc” experts. At best, the issue remained to be decided. In any event, the precise point had not been taken at trial and leave to do so was refused in the appeal.

Where an issue arises as to the state of specialised knowledge of some particular issue at some time in the past, an expert in that particular field (even though not an expert at that time) is permitted to give evidence, based on the literature of that particular time, as to what that state of knowledge was at that time: BI (Contracting) Pty Ltd v University of Adelaide [2008] NSWCA 210 at [20]–[26].

[4-0635] Specialised knowledge of child development and behaviour: s 79(2)

Section 79(2) was inserted by the Evidence Amendment Act in order to “avoid doubt” in order to include within the term “specialised knowledge” such knowledge relating to child development and child behaviour (including specialised knowledge of the impact of sexual abuse on children and their development and behaviour during and following the abuse), and (see ALRC Report 102 at [9.138]) in order to encourage the admission of such evidence in appropriate circumstances. The Australian Law Reform Commission did not consider that the provision represented any major departure from existing law, and said that it had been proposed in order to “clarify the position” (ALRC Report 102 at [9.156]).

There is little case law on the application of s 79(2), however see further two Victorian cases MA v R (2013) 40 VR 564 and De Silva v DPP (2013) 236 A Crim R 214 which dealt with s 108C(1) (exception to the credibility rule) which is in like terms to s 79(2). De Silva stated at [26] that the purpose of such evidence is “educative”: to impart specialised knowledge the jury may not otherwise have, in order to help the jury understand the evidence of and about the complainant, and so as therefore to be better able to evaluate it.

Section 108C in Pt 3.7 (Credibility) also makes provisions relating to this type of evidence.

[4-0640] Ultimate issue and common knowledge rules abolished — s 80

The intention of the Law Reform Commission was to abolish the “ultimate issue rule”: ALRC Report 26, vol 1, par 743. The section does not make the evidence admissible unless it is relevant to a particular issue; it merely removes the fact that the evidence goes to an ultimate issue from the reasons for which a court must or could exclude that evidence: Idoport Pty Ltd v National Australia Bank Ltd (2000) 50 NSWLR 640 at [39].

The Evidence Act has been interpreted as having successfully abolished the rule, but it has been stressed that judges should exercise particular scrutiny when experts move close to the ultimate issue, lest they claim expertise outside their field or express views unsupported by disclosed and contestable assumptions: R v GK (2001) 53 NSWLR 317 at 326–327, [40]; Adler v ASIC (2003) 46 ACSR 504 at [622], [629]; Forge v ASIC (2004) 213 ALR 574 at [264]–[278]. (This issue was not raised in the appeal to the High Court: Forge v ASIC (2006) 228 CLR 45 at [48], [120], [242], [279].)

Section 80 deals only with the admissibility of expert evidence (that is, opinion evidence) in relation to a fact in issue or an ultimate issue; it does not affect the practical wisdom of a firm rule that the likelihood of conduct being misleading or deceptive where the sales are to the general public is a question for the tribunal of fact and not for any witness to decide, but it is otherwise when the sales are in specialised markets concerning persons engaged in a particular trade: Interlago AG v Croner Trader Pty Ltd (1992) 111 ALR 577 at 617; Cat Media Pty Ltd v Opti–Healthcare Pty Ltd [2003] FCA 133 at [55]; Domain Names Australia Pty Ltd v .au Domain Administration Ltd (2004) 139 FCR 215; Pan Pharmaceuticals Ltd (in liq) v Selim [2008] FCA 416 at [34].

In Adler v ASIC, above, the Court of Appeal expressed reservations (at [273]) about an expert in director’s duties being asked to give his opinion as to whether the defendant had acted honestly. In Yates Property Corp Pty Ltd (in liq) v Boland (1998) 157 ALR 30 at 56, the Full Federal Court sought to discourage expert evidence being given on the issue of negligence by legal practitioners, suggesting that, if such evidence is tendered by reason of s 80, the only appropriate use to which it should be put is to confirm the views of the court on a particular issue rather than to inform those views. In Minnesota Mining and Manufacturing Co v Tyco Electronics Pty Ltd [2002] FCAFC 315 at [50], the same court similarly said that expert evidence in a patent case as to whether a claimed invention was obvious or did not involve an inventive step will of necessity be essentially argumentative and, even if admissible, will result in a waste of time and is therefore a prime candidate for the application of s 135 of the Evidence Act.

At common law, expert evidence was not admissible to establish matters which the tribunal of fact could determine for itself or formulate its own empirical knowledge as a universal law: Clark v Ryan (1960) 103 CLR 486 at 491; the evidence was admissible only if it assisted the tribunal of fact on matters outside its experience and knowledge without usurping its function: Murphy v The Queen (1989) 167 CLR 94 at 110–111, 129–130. The Law Reform Commission intended to permit expert evidence — for example, on the behaviour of a “normal” person — so long as it is relevant: ALRC Report 26, vol 1, par 743. Such evidence, though admissible, will be excluded in the exercise of the court’s discretion pursuant to s 135 or s 137 if there is a risk that the jury will defer to the expert’s opinion rather than make up its own mind: R v Smith (2000) 116 A Crim R 1 at [69]–[71]; Keller v R [2006] NSWCCA 204 at [43]; Cadbury Schweppes Pty Ltd v Darrell Lea Chocolate Shops Pty Ltd (2007) 239 ALR 662 at [54]–[55].

Expert opinion evidence is not inadmissible because it is a matter of common knowledge: Cadbury Schweppes Pty Ltd v Darrell Lea Chocolate Shops above, at [54]; nor is it restricted to issues that are outside the knowledge or experience of ordinary persons: at [57] (The refusal of special leave to appeal to the High Court was not related to this issue: [2007] HCA Trans 468.)

Expert evidence directed to answering a question of law or fact that is directly before the court for decision is likely to be inadmissible not because it goes to the ultimate issue but because it will not be wholly or substantially based on the expert’s specialised knowledge or because it will be irrelevant: ASIC v Vines [2003] NSWSC 1095 at [27]; Forge v ASIC (2004) 213 ALR 574 at [272] (the issue did not arise in the appeal to the High Court: Forge v ASIC (2006) 228 CLR 45).

In a fraud trial where an issue is whether there was an arguable case that private tax rulings were incorrect in law, evidence is admissible to show what the law is: R v Petroulias (2005) 62 NSWLR 663 at [28].

Where an opinion is given by reference to a legal standard, it is essential, before the opinion is admissible, and “certainly before any weight can be afforded to it, that the expert’s understanding of the relevant legal standard be established and be shown to be in accordance with the law”: Pan Pharmaceuticals Ltd (in liq) v Selim [2008] FCA 416 at [36].

Opinions based on the expert witness’s own interpretation of the evidence are not inadmissible, provided that the reasoning process is properly explained and is shown to depend on the expert’s specialised knowledge: ASIC v Rich (2005) 53 ACSR 110 at [289]–[291].

[4-0650] Time limit on notice

Evidence Act s 177(2) provides that evidence of a person’s opinion may be adduced by tendering an expert’s certificate. However it is necessary to serve the opinion and certificate 21 days before the hearing, unless the court allows a different period for service: s 177(3)(a) and (b).

In Director of Public Prosecutions v Streeting [2013] NSWSC 789, Davies J considered these provisions, holding that the magistrate in the court below had not erred in refusing an adjournment to enable the prosecutor to remedy the failure to serve the relevant certificate within the specified time.


  • Evidence Act 1995, ss 76, 77, 78, 79, 80, 135, 137, 177

Further References

  • S Odgers, Uniform Evidence Law, 18th edn, Thomson Reuters, Sydney, 2023

  • J Heydon, Cross on Evidence, 14th edn, LexisNexis Butterworths, Sydney, 2024

  • R Weinstein, J Anderson, J Marychurch and N Wooten, Uniform Evidence Law in Australia, 4th edn, LexisNexis Butterworths, 2023

  • ALRC Report 26, vol 1, Australian Government Publishing Service, Canberra, 1985

  • ALRC Report 38, Australian Government Publishing Service, Canberra

  • ALRC Report 102, Australian Government Publishing Service, Canberra, 2005