Tag: Opinion

When will an expert’s opinion be shown to be based on their specialised knowledge?: Lang v The Queen [2023] HCA 29

In Lang v The Queen, the High Court considered whether a forensic pathologist’s opinion – that the deceased’s wounds were more likely inflicted by another person than self-inflicted – was founded on their expert knowledge within the field of forensic pathology (and thus, whether the opinion was admissible as expert opinion evidence).

Lang was heard on appeal from the Court of Appeal of Queensland. There were two grounds of appeal in both the Court of Appeal and the High Court, though this post is concerned only with the second ground, which was that a miscarriage of justice was caused by the wrongful admission of the forensic pathologist’s evidence at trial.

The appellant argued that the opinion evidence from Dr Ong (the forensic pathologist) was inadmissible because it was not demonstrated to be based on his expert knowledge in forensic pathology.

Ultimately, a majority of the High Court (Kiefel CJ, Gageler and Jagot JJ, Gordon and Edelman JJ in dissent) dismissed the appeal, noting as to the second ground that:

‘… we cannot conclude that, in engaging in the process of reasoning which led to the formation of the opinion, Dr Ong did other than draw substantially on his specialised knowledge.’ (Kiefel CJ and Gageler J at [26])

and

‘It is clear from a fair reading of the transcript of Dr Ong’s evidence that the impugned evidence was based on his specialist knowledge and reflected the combined effect of that knowledge brought to bear on multiple facts that he could ascertain only by reason of his specialist expertise…’ (Jagot J at [469])

As an appeal from Queensland, this case concerns the common law of evidence. However, as stated by Kiefel CJ and Gageler J in their joint judgment (at [11]), the relevant requirement (for the expert’s opinion to be shown to be based, at least substantially, on their specialised/expert knowledge) applies equally under the Uniform Evidence Law.

BACKGROUND

The deceased died from blood loss secondary to a stab wound to her abdomen. The only two people in the deceased’s apartment at the time of her death were the deceased and the appellant. It was accepted at trial that there were only two possible explanations for her death: either the deceased was killed by the appellant, or the deceased died by suicide. The prosecution case at trial was the former explanation.

In support of their case, the prosecution adduced evidence from a forensic pathologist, Dr Ong (who had performed an autopsy of the deceased and produced a postmortem report based on that autopsy), that the deceased’s wounds were more likely to have been inflicted by another person than self-inflicted. Dr Ong’s evidence was adduced over objection made by the appellant and ultimately found to be admissible by the trial judge in a pre-trial hearing.

The appellant accepted that forensic pathology was a field of expertise, that Dr Ong was an expert in forensic pathology, and that the question of whether wounds may have been self-inflicted or inflicted by another was capable of being the subject of expert evidence if ‘a suitable foundation as to the [witness’s] training, study or experience has been laid’. Therefore, the crux of the issue was whether or not the opinion was shown to be based on Dr Ong’s expert knowledge.

Dr Ong said he took a number of factors into account in reaching the opinion that the wound was more likely to have been inflicted by another person than self-inflicted, such as the absence of evidence of self-harm (for example, incisions to the wrist). Dr Ong said that the factor he took most into account in forming his opinion was ‘the multiplicity of the stab wounds’ and the ‘rotation of the blade’.  Dr Ong gave evidence that there was a single penetrating stab wound, comprised of two internal thrusts of the knife in one direction, a partial retraction and rotation of the knife while it was mostly withdrawn from the deceased’s body, followed by a further two or three thrusts, with the knife rotated in a different direction to that of the first two thrusts. There was a single point of entry.

Critically, Dr Ong said in his evidence-in-chief in the pre-trial hearing that his opinion was based on his ‘logical sense of what happened’. In cross-examination at trial, Dr Ong said he had found no literature on a wound bearing the same features as the deceased’s (featuring as it did a single entry external wound, a couple of internal stabs, rotation, and then a couple of more internal stabs). He said had also not dealt with a case like this in his career.

The appellant submitted that Dr Ong’s opinion was, therefore, substantially based on his subjective view as to how a person may or may not act when attempting to die by suicide, rather than being properly based on his special expertise in forensic pathology.

JUSTICE JAGOT’S JUDGMENT

The leading judgment was written by Jagot J, with which Kiefel CJ and Gageler J agreed. Justice Jagot found that Dr Ong’s opinion was not based on his subjective view of human behaviour (a matter beyond his expertise) – rather, the conclusion that the wounds were more likely to be self-inflicted was based on the wounds themselves and his experience as a forensic pathologist. Justice Jagot relevantly said:

‘It is apparent that Dr Ong was not purporting to give evidence as to the deceased’s psychological state or, indeed, the psychological state of any person who ends their own life. He was explaining that the evidence of the wounds themselves…, based on his expertise and experience over 25 years, led him to the conclusion that the wounds were more likely to be inflicted by another person than to be self inflicted. It is because drawing conclusions from wound patterns involves a process of deductive reasoning based on expertise as a forensic pathologist, and because he had no expertise to opine as to the particular psychology of the deceased at the time of the infliction of the wounds (and did not so opine), that he could not rule out the possibility that the wounds were self inflicted.’ (at [468])

As to whether Dr Ong could form such a conclusion without having encountered an identical case in his experience or in the literature, Jagot J said that ‘the essence of expertise is the capacity to reason from facts based on specialist training, study, or experience’ (at [469]):

‘… The fact that Dr Ong had not identified such a sequence of events in either a suicide or a homicide caused by stabbing does not mean that his evidence was not based on his expertise and does not mean his evidence lacked a rational foundation… it is highly unlikely that any case of suicide or homicide reported in the literature will be identical to an actual case which confronts a forensic pathologist… He is entitled to bring to bear all his specialist training, study, or experience to form an opinion without being able to point to an identical or even similar case. It is clear… that the impugned evidence was based on his specialist knowledge and reflected the combined effect of that knowledge brought to bear on multiple facts that he could ascertain only by reason of his specialist expertise…’ (at [469], emphasis added)

Justice Jagot thus dismissed the ground of appeal.

CHIEF JUSTICE KIEFEL AND GAGELER J’S JUDGMENT

Chief Justice Kiefel and Gageler J agreed with Jagot J, but wrote separately from the lead judgment to elaborate on the common law principles which bore on the admissibility of Dr Ong’s opinion.

In particular, their Honours discussed the requirement for an expert witness to reveal to the court their process of reasoning, so as to demonstrate that their opinion is based on application of their specialised knowledge to the relevant facts. Drawing on Makita (Australia) Pty Ltd v Sprowles [2001] NSWCA 305, as applied in Dasreef Pty Ltd v Hawchar [2011] HCA 21, Kiefel CJ and Gageler J noted that:

‘…in order to satisfy the condition of admissibility that the opinion of an expert be demonstrated to be based on specialised knowledge or experience, the inference drawn by the expert which constitutes the opinion [must] be supported by reasoning on the part of the expert sufficient to demonstrate that the opinion is the product of the application of the specialised knowledge of the expert to facts which the expert has observed or assumed.’ (at [11])

Their Honours noted that this requirement exists both at common law and under the Uniform Evidence Law (at [11]). They also noted that the standard set explicitly by the Uniform Evidence Law – that an expert’s opinion need only be ‘substantially based on’ their specialised knowledge – applies equally at common law (at [12]).

Their Honours also noted that for the purposes of admissibility, the relevant question is simply whether the process of reasoning is sufficient to demonstrate that their opinion is the product of the application of their expert knowledge to the facts. Whether or not the reasoning is clear and convincing does not go to admissibility, but is relevant to how much weight the fact-finder might afford to the opinion:

‘Here, it is important to highlight a distinction touched on but not elaborated upon in Makita. The distinction is between the present question as to whether a process of reasoning engaged in by an expert is sufficient to demonstrate that his or her opinion is the product of the application of specialised knowledge and the question of the extent to which a process of reasoning engaged in by an expert through the application of specialised knowledge is clear and convincing. Both questions can be described as going to the utility or value of the opinion. However, it is the present question alone that goes inexorably to the “admissibility” of the opinion as distinct from its “weight”. In addressing the present question of whether the opinion satisfies the condition of admissibility that the opinion be demonstrated to be based on specialised knowledge or experience of the expert, lack of cogency in so much of the reasoning as is found to involve application of specialised knowledge is not to the point: “the giving of correct expert evidence cannot be treated as a qualification necessary for giving expert evidence”.’ (at [15]–[16])

Chief Justice Kiefel and Gageler J went on to note that the cogency of an expert witness’ reasoning could affect the admissibility only if and when a court is called upon to decide whether its probative value is outweighed by its prejudicial effect (ie, when applying the Christie discretion at common law, or ss 135/137 of the Uniform Evidence Law).

It is of particular interest that their Honours said ‘assessing the probative value of the opinion [by] having regard to the cogency of the reasoning proffered in evidence in support of it involves no departure from the now settled principle that the assessment of the probative value of evidence requires that evidence to be “taken at its highest”: taking evidence at its highest involves making no assumption that the evidence in question is convincing’ (at [17]). Though these principles have been stated and settled previously, it is worth noting the inherent difficulty – at least in some cases – involved in teasing apart notions of credibility and general reliability (which are not to be considered when determining probative value) from the cogency of the reasoning (which can be considered as going to probative value).      

Turning to consider the case at hand, their Honours said ‘The overwhelming impression which emerges from reading the transcript is that of a professional and dispassionate forensic pathologist seeking to make sense of observed phenomena in respect of which neither his long experience nor his wide reading furnished an exact precedent.’ (at [20])

As to Dr Ong’s statement that he formed his opinion based on his ‘logical sense of what happened’, their Honours noted that ‘This expression was unfortunate in that it could be interpreted as Dr Ong saying that, in forming his opinion, he had drawn on some third source of background knowledge additional to his professional experience and the scientific literature. However, it is clear enough… that what he was saying was that he had engaged in a process of inductive reasoning which involved applying his knowledge of the interpretation of stab wounds to observed features of [the deceased’s] wound to form a conclusion about which of the two scenarios was more likely.’ (at [21])

Chief Justice Kiefel and Gageler J acknowledged that at trial, Dr Ong perhaps did not do a particularly good job of explaining why the wounds were more consistent with stabbing by another than they were with stabbing oneself. Their Honours said that ‘Absent a clearer explanation of Dr Ong’s process of reasoning, his opinion about whether the features of the wound which he identified were more consistent with stabbing by someone else might legitimately have been thought to have carried [little weight]… That weakness might well have been thought to have gone to the admissibility of Dr Ong’s opinion had the argument been advanced that its probative value was outweighed by its prejudicial effect.’ (at [25])

However, the argument put by the appellant was instead that the reasoning was not sufficient to demonstrate that the opinion was based on Dr Ong’s expert knowledge, and on that point Kiefel CJ and Gageler J agreed with Jagot J that the ground of appeal should be dismissed.    

CONCLUDING COMMENT

This case is interesting and helpful for a number of reasons. It provides a solid illustration of an opinion which is demonstrated to be based on expert knowledge even though the process of reasoning was not particularly clearly expressed. To that extent, it also demonstrates the distinction between ‘sufficient reasoning’ to demonstrate that the opinion is substantially based on expert knowledge, as compared to ‘cogent or convincing reasoning’ which chiefly goes to weight but can also affect probative value.

The case is also interesting because it speaks to and demonstrates a number of commonalities between the common law and Uniform Evidence Law tests for admissibility of expert opinion. A consequence of this is also that it is relevant to those practicing in all Australian jurisdictions – ie, it is presently relevant in Western Australia, and will continue to be relevant if/when the Uniform Evidence Law is adopted here.

This post is jointly authored by Julia Symons and Aidan Ricciardo

The State of Western Australia v Quartermaine [2020] WASC 458

Background:
This decision relates to a trial by judge alone before Hall J. The accused was charged with murder, and prior to the trial, admitted that he had unlawfully killed the victim. However, the defence argued that intent could not be proved beyond reasonable doubt (‘having regard to all the circumstances, including the intoxicated state of the accused’), and that therefore the accused could only be found guilty of a lesser offence ([4]).

During the trial, Hall J was required to determine whether the defence’s expert psychiatric evidence was admissible. This issue arose because the expert opinion was partially based on information which was not supported by sworn evidence. The issue is set out at [145]-[146]:

‘The accused elected not to give evidence. That was his right and no adverse inference can be drawn from that fact. However he did call expert evidence from Dr Victoria Pascu, a forensic psychiatrist.

Dr Pascu interviewed the accused at Hakea Prison and relied on information provided by him for the purpose of forming her conclusions. Some of the information provided by the accused reflected evidence that was otherwise available. However, the accused also provided Dr Pascu with some information, including in regard to his drug and alcohol usage generally and on the night in question, that was either not supported by the evidence or was inconsistent with it. This created an issue as to the extent to which Dr Pascu’s opinions were based upon information that was not supported by sworn evidence. An objection by the prosecution was taken to Dr Pascu’s evidence on this basis.’ (emphasis added)

In essence, the accused’s choice not to give evidence meant that he did not confirm on oath what he had said to Dr Pascu. This meant that some of the foundation of Dr Pascu’s opinion was not supported by any admissible evidence at trial, in that what the accused said to Dr Pascu was hearsay.

During the trial, Hall J decided that the evidence could be led, subject to any findings about weight, because Dr Pascu confirmed that it would be possible for her ‘to exclude the information that had been provided by the accused and to only rely upon the evidence before the court, including the accused’s interview with the police’ ([147]).

Reasons:
Justice Hall provided detailed reasons for his decision in the judgment, concluding that:

‘In this case prior to Dr Pascu being called she was asked whether it would be possible for her to put aside the information that was provided to her by the accused and whether she would still be able to give an opinion as to [the fact in issue]. She advised that she could do this. In these circumstances I concluded that Dr Pascu’s evidence would not be based entirely on inadmissible material and that insofar as she had partly relied upon any information from the accused which had not been confirmed on oath then that would reduce the weight to be accorded to her opinion.’ ([159])

As the opinion did not wholly rely on hearsay, it was still admissible. The extent of reliance on inadmissible hearsay ‘was able to be explored in cross‑examination and is relevant to the weight to be given to her opinion’ ([152]).

Comment:
This decision is of interest for the practical application of the (sometimes unclear) ‘factual foundation’ or ‘factual basis’ rule – even the nature of which is still subject to some disagreement, as some regard it as a formal rule for admissibility and others regard it as more of a practical requirement in that an opinion without an admissible factual basis cannot be of any weight. The common law authorities relating to this rule are contradictory, so Hall J’s discussion of the principle is helpful to understand which authorities are to be preferred.

In this regard, his Honour cites at [158] (inter alia, and apparently with some approval) the following passage from Ipp J’s judgment in Pownall v Conlan Management Pty Ltd (1995) 12 WAR 370:

‘[E]xpert opinion based entirely on inadmissible evidence is itself inadmissible and there is no discretion to admit it. I form this view as to admit such an opinion would be to admit, indirectly, the inadmissible evidence itself. If an opinion, based solely on evidence that the court by law is required to exclude, is itself admitted, the inadmissible evidence would have some influence over the court’s decision. Such a result would defeat the purpose of the law that excludes the inadmissible evidence. If the primary facts on which the evidence is based are not admissible, the opinion is valueless and irrelevant and, in my opinion, should be excluded... It is only when the primary facts upon which the opinion has been based are established that the opinion should be admitted into evidence.

On the other hand, where the expert opinion is based only partly on inadmissible testimony and that inadmissible testimony can readily be ascertained and discarded, the opinion should be admitted subject to weight.’ (emphasis added)

The judgment:
The judgment was delivered on 11 December 2020 and can be accessed here. See especially paragraphs [145]–[159] for discussion relating to admissibility of the evidence.