Staying inside the lines – the importance of properly instructing experts

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In the matter of R v BDI [2020] QCA 22, the appellant was convicted at trial of various rape and assault offences, including sexual offending against his biological daughter. He appealed against his conviction on several bases, including that the evidence at trial of a psychiatric expert, Dr Tracey, was inadmissible and that the trial judge failed to direct the jury properly as to how they could use the doctor’s evidence.

The case highlights the importance of instructing experts to comment only within their field of expertise.

Between October 2014 and December 2014, the appellant’s daughter was diagnosed as suffering from drug-induced psychotic episodes, which she was cross-examined about at trial. The Crown called Dr Tracey to give evidence. He had not personally treated the daughter, but was a consultant psychiatrist for the acute care team at the hospital where she was treated.

He provided a summary of what had occurred while the daughter had been an inpatient, based upon her medical records, which he had reviewed. He also provided his medical opinion as to the meaning of drug-induced psychosis and its symptoms, as well as the general duration of, and appropriate treatment for, the condition. In that regard, he commented specifically on the effectiveness of the treatment given to the daughter. [6]

His evidence was not objected to at trial, nor were his opinions challenged. He was cross-examined by the defence, who attempted to draw admissions as to the effects of drug-induced psychosis and the subsequent unreliability of the daughter’s evidence inasmuch as she may not have been able to distinguish between hallucination and reality when it came to the alleged sexual assault.[6]

On appeal, the appellant complained that Dr Tracey, who was a non-treating doctor, read slabs of medical reports, some of which were claimed to be inadmissible, and that the trial judge did not give the full direction to the jury in relation to expert evidence. However, the trial judge had not been requested to give any redirection in that respect.[44]

The appeal court found that the expert evidence given by Dr Tracey as to the nature of substance-induced psychosis and its resolution was relevant and a matter well within his expertise. Further, it was specialised information likely to be outside the experience and knowledge of a judge or jury. Importantly, his evidence did not extend to any opinion on the credibility or reliability of the allegations made by the daughter.[52]

The Tactical Appeal

At trial, the defence had hoped to obtain a tactical advantage through the evidence of Dr Tracey by using his evidence of the daughter’s drug-induced psychotic episodes as a means of discrediting her. On appeal, the appellant argued that instead the doctor’s evidence may instead have acted to boost the credibility of the daughter because the jury could have believed that her mental health disorders resulted from stress and substance abuse arising from the sexual offending against her.[41]

However, no objections had been taken at trial to the documents Dr Tracey relied upon for his evidence, and he was also extensively cross-examined by the defence, who also relied upon the doctor’s evidence in its summing up to the jury.[43]

The appeal court found that Dr Tracey’s evidence did not prejudice the appellant at trial. Indeed, the Crown had sought to marginalise the relevance of the doctor’s evidence to the daughter’s reliability and the defence had relied upon it to attack the daughter’s reliability. The appeal court therefore found no reason to consider that the appellant was in any way prejudiced by the doctor’s evidence, such that it may have denied the appellant a fair chance or even possibility of obtaining an acquittal.[57]

The Directions Appeal

The appellant made the further complaint that the directions given by the trial judge to the jury regarding Dr Tracey’s evidence were not in accordance with the Practice Direction for expert evidence and did not direct the jury that it was a matter for them to accept or reject the facts underlying the opinion. On that basis, the appellant argued that there was a miscarriage of justice arising from the risk that the jury might have improperly reasoned that, as Dr Tracey was an expert, they should accept his opinions.[59]

However, as Dr Tracey did not give any opinion about the daughter’s credibility or how her mental state could have affected the truth of her allegations, the appeal court found that there was no risk of the jury reasoning backwards from his evidence in that way.[66]

Although the trial judge did not give the entire direction regarding expert witnesses that appeared in the Court’s Bench Book, his summing up dealt with the competing contentions of the Crown and defence as to the relevance of Dr Tracey’s evidence, making it clear that it was entirely a matter for the jury whether they considered the complainant’s mental health did or did not affect the reliability of her evidence.[66]

Further, the judge’s directions made it clear that the truth and reliability of the complainant’s account of the allegations was a matter for the jury. Accordingly, there was no risk that the jury would have reasoned impermissibly from the evidence of Dr Tracey that his evidence bolstered the complainant’s evidence or could be used to negate any doubt they had about her evidence.

Consequently, the appeal court found that the failure to give the full direction regarding expert evidence did not deny the appellant a fair trial, nor affect the verdict so as to deny the appellant of a chance of an acquittal.[67]


The case illustrates the importance of expert witnesses staying within their field of expertise and lawyers similarly confining the questions they ask experts.

The appellant tried to claim that Dr Tracey’s evidence influenced the jury’s opinion of the daughter’s credibility and denied him a fair outcome. However, the doctor had given no opinion about that matter, staying only within the bounds of his expertise.

The fact that Dr Tracey’s report commented only upon the objective matters relating to drug-induced psychosis and did not opine on how the circumstances and treatment of the daughter may have affected her credibility meant that the appellant’s arguments about the doctor’s evidence impermissibly influencing the jury’s opinion were dismissed.

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