HKSAR v McCall, Howard Kenneth and another

In HKSAR v McCall, Howard Kenneth and another (HCCC 446/2016 – 27 October 2017) Deputy High Court Judge Andrew Bruce SC ruled that the opinion evidence of a specialist psychiatrist on consumption rates of certain drugs, as sought to be adduced by the prosecution, was inadmissible.  In his ruling, the learned Deputy High Court Judge revisited the principles and authorities governing the reception of expert opinion evidence.

Facts and Arguments

D1 and D2 were charged with 3 counts of trafficking in dangerous drugs involving various kinds of drugs.  D1 was a British Caucasian and D2, a Thai national.  D1 objected to the reception into evidence of the psychiatrist concerning the average daily consumption rates of various types of drugs and by whom. The focus of the objection was on the sufficiency of qualification and expertise by the specialised psychiatrist as to average consumption rates of the different drugs in question and by which ethnic groups.


  • The learned Deputy High Court Judge summarised the principles governing the reception into evidence of expert opinion as follows:-
    • The evidence is relevant to the issue(s) before the court.
    • The subject matter is a recognised field of science, art or learning which is capable of being made the subject of study experience or research and in which a person can (by study, experience or research) become expert or skilled.
    • The person proposing to give the evidence is sufficiently qualified or expert in his field.
    • The area for consideration is one where the tribunal requires the assistance of an expert.
  • With regard to the sufficiency of qualifications or expertise, two issues are critical to the admissibility of expert evidence: (i) whether the Court could be satisfied that the witness possesses the necessary qualifications; and (ii) the scope of the expertise that the proposed witness may bring to bear on the topic.
  • The opinion must not extend beyond the scope of this expertise and the expert report must demonstrate how the opinion relates to his expertise.
  • Expert witnesses may rely on studies or tests done by others. However, the publications of others are not evidence of the truth of the data.


  • In this case, the psychiatrist relied on two studies from Taiwan and China on consumption rates of drug abusers. Whether his own expertise and experience as a psychiatrist extended to consumption rates by drug abusers in Hong Kong was open to question.
  • Statistical validity and relevance to Hong Kong of the two studies were critical to his evaluation. The psychiatrist did not reveal whether he was equipped by training or experience to make such an evaluation.  The necessary statistical validity and relevance would not be met simply by some anecdotal experience which accorded with studies in China and Taiwan.
  • There were other limitations to the psychiatrist’s evidence: (a) the limit of his experience – only in the context of treating mental illness; (b) the lack of a basis for the evaluation unfettered by explanation; and (c) the scope of the subjects of the two studies – ethnic Chinese (whereas D1 & D2 were non-Chinese).
  • Having considered that the potential benefits of the reception into evidence of the specialist psychiatrist would dramatically outweigh the potential risks, the learned Deputy High Court Judge ruled the evidence on consumption rates was inadmissible.


This ruling warns of the danger of permitting into evidence expert evidence without proper checks and gatekeeping. The learned Deputy High Court Judge stressed the role of the Court as the gatekeeper, which gatekeeping goes beyond whether the proposed evidence is more prejudicial than probative.

It also illustrates an apparent need for authoritative studies on consumption rates in Hong Kong.  Expert opinion on consumption rates of drugs is often relied upon by the prosecution in drug-trafficking cases, with an invitation to the jury that an inference of trafficking rather than self-consumption possession can be more readily drawn.  This ruling stresses the need for circumspection in assessing the admissibility of such evidence.

This case was handled by our Christopher Morley and William Johnson instructing John McNamara. The Defendant was acquitted of all drug-trafficking charges.