AuthorJeffrey PINSLER SC LLB (Liverpool), LLM (Cambridge), LLD (Liverpool); Barrister (Middle Temple); Advocate and Solicitor (Singapore); Professor, Faculty of Law, National University of Singapore.
Publication year2022
Citation(2022) 34 SAcLJ 10075
Published date01 March 2022
Date01 March 2022
I. Introduction

1 This article concerns the intersection between expert opinion and hearsay evidence. It is a long-established rule — the rule against hearsay — that the facts which form the basis of an expert's opinion must be admissible.2 These facts may be within the expert's personal knowledge (in which case he can testify about them), or be proved by another witness who has personal knowledge of those facts, or by admissible documents and/or real evidence.3 Evidential challenges may arise when the expert relies on facts referred to in documents or another person's or entity's oral information if the documents are not properly proven or the other person does not testify in court. The hearsay rule applies to the expert as it does to any witness. However, the common law makes a distinction between information and knowledge which the expert has acquired from various sources during his professional career (“professionally acquired information”) and facts in issue of which the

expert has no personal knowledge (“primary facts”). While primary facts must be proved, professionally acquired information does not (although relevant information must be included in the expert's report).4 Professionally acquired information would ordinarily include the expert's own professional experience, the knowledge and learning he has acquired from his research and training throughout his career including information gained from books, articles, papers, reports and other materials (whether published or not)5 concerning his area of expertise, and input from his professional colleagues and others involved in the course of his work.
II. Examination of the case law

2 Although professionally acquired information is technically hearsay (because the expert's reliance on it expressly or impliedly asserts that it is truthful), the hearsay rule is relaxed in these circumstances “in the interest of logistical practicality”, as Sundaresh Menon CJ put in Anita Damu v Public Prosecutor6 (“Anita Damu”). It would be extremely burdensome (if not impossible) for a party to adduce direct evidence of the truth of all the information which that party's expert has accumulated in the course of his career. As Menon CJ put it: “[I]t would be impractical to require in every instance that those other professionals [whose information the expert relies upon] also give evidence of their work, even though this might technically constitute general hearsay evidence.” The principle that the rule against hearsay does not apply to professionally acquired information relied on by an expert to provide an opinion was affirmed early on in English Exporters Pty Ltd v Eldonwall7 (“English Exporters”) in which Megarry J considered the position of an expert giving his opinion on rental value:8

As an expert witness, the valuer is entitled to express his opinion about matters within his field of competence. In building up his opinions about values, he will no doubt have learned much from transactions in which he has himself been engaged, and of which he could give first-hand evidence. But he will also have

learned much from many other sources, including much of which he could give no first-hand evidence. Textbooks, journals, reports of auctions and other dealings, and information obtained from his professional brethren and others, some related to particular transactions and some general and indefinite, will all have contributed their share … Nevertheless, the opinion … is none the worse because it is in part derived from the matters of which [the valuer] could give no direct evidence.

3 Megarry J did not consider this professional information to be hearsay evidence: “No question of giving hearsay evidence arises in such cases, the witness states his opinion from his general experience.”9 The learned judge contrasted these circumstances to the situation in which the expert gives evidence of facts in issue in the case of which he has no personal knowledge.10 With respect, the learned judge's characterisation of professionally acquired information as not being hearsay is not correct. Professionally acquired information is hearsay to the extent that the expert relies on the information on the assumption that it is true. However, as such information does not concern the primary facts of the case, it does not attract the full rigour of the hearsay rule. Later English cases would regard the professionally acquired information as “general hearsay” which, despite the hearsay rule, is admissible. This was confirmed by Menon CJ in Anita Damu.11

4 In R v Abadom,12 the English Court of Appeal endorsed the distinction made by Megarry J in English Exporters between professionally acquired information (which can be admitted despite the hearsay rule) and primary facts that have to be proved by admissible evidence. The appellant was charged with robbery. It was alleged that the appellant (and others) broke into a family office and that he shattered a window to cause fright. Subsequent to his arrest, shoes retrieved from his residence were found to have fragments of glass attached to and embedded in them. Identity was an issue in this case because the appellant was wearing a balaclava helmet during the robbery. One of the two expert witnesses (“E1”) called by the prosecution testified that he had chemically analysed the fragments of glass connected to the shoes and the glass from the window. E1 found that they were similar. The second expert witness (“E2”) compared several of the fragments of glass found in and on the shoes with each other and with the glass from the window and determined they all had identical refractive index. Having taken into account E1's chemical analysis and having consulted statistics

of the refractive index of broken glass analysed in forensic laboratories,13 E2 opined that the refractive index of the glass from the shoes and the window occurred in 4% of analysed glass. He concluded14 that there was “very strong evidence that the glass from the shoes [was] the same as the glass from the window, in fact it originated from the window”. On appeal, the appellant argued that E2 had based his opinion on hearsay (that is, the statistics were collated by persons not called as witnesses). The Court of Appeal held that E2 was entitled to ground his opinion on the statistics:15

As an expert in this field [E2] was entitled to express an opinion on this question, subject to laying the foundation for his opinion and subject, of course, to his evidence being tested by cross-examination for evaluation by the jury. In the context of evidence given by experts it is no more than a statement of the obvious that, in reaching their conclusion, they must be entitled to draw upon material produced by others in the field in which their expertise lies.

5 The Court of Appeal summed up the principle as follows: “We are here concerned with the cogency or otherwise of an opinion expressed by an expert in giving expert evidence. In that regard it seems to us that the process of taking account of information stemming from the work of others in the same field is an essential ingredient of the nature of expert evidence.”16 The position would have been different if E2 had not based his determination of the refractive index of the glass on his own personal knowledge and E1's chemical analysis of it and, instead, relied on information given to him out of court. This is because E2 would then be purporting to prove primary facts about which he had no personal knowledge: “[I]t would no doubt have been inadmissible if [E2] had said in the present case that he had been told by somebody else that the refractive index of the fragments of glass and of the control sample was identical, and any opinion expressed by him on this basis would then have been based on hearsay.”17 The court went on to state that if E2 had not himself ascertained the refractive index, the person who had done so would have needed to testify prior to E2 giving his opinion.

6 Although English Exporters and Abadom were not referred to by Chan Seng Onn JC (as he then was) in Gema Metal Ceilings (Far East) v Iwatani Techno Construction (M)18 (“Gema Metal”), the learned judge

applied the common law principles for the first time in Singapore. The case concerned the design of a metal strip ceiling system which had been supplied by the plaintiff to the defendant. In response to the plaintiff's claim for the price of the strip ceiling system, the defendant claimed that it was not of merchantable quality and not fit for its purpose. The defendant's expert (a civil engineer) gave his opinion that the design was defective. He relied on his assessment of certain reports and the results of tests carried out by a firm in Hong Kong. The expert was not involved in any of the tests and was not in attendance when they were conducted. As the makers of the reports were not called to prove the primary facts and none of the exceptions to the hearsay rule applied,19 the reports were inadmissible hearsay.20 Chan JC acknowledged that professionally acquired information (“general hearsay” as opposed to “specific hearsay”) would not be subject to the strict application of the hearsay rule:21

I recognise that most experts frequently employ hearsay to some degree in forming their views. In fact, as a matter of convenience, courts have sometimes tended not to insist upon proof of the extrinsic materials customarily employed by experts to perform their work, namely understanding obtained from the use of professional libraries and knowledge acquired in the discharge of professional duties.

7 Furthermore, the learned judge excluded the parts of the expert opinion that relied on the reports: “Where an expert seeks to give an opinion the basis of which is dependent upon the truth of hearsay evidence, that expert's evidence is likewise inadmissible.”22 Consequently, “an expert is only permitted to give his opinion when the primary facts upon...

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