Reliance upon other opinions as a basis for expert opinion
44 A central issue underlying the State's objections to Dr Martin's Revised Report concerns Dr Martin's reference to the Additional Materials. The State submitted that the Additional Materials, containing the opinions of other anthropologists who are not being called as witnesses in the proceeding, are not admissible evidence and cannot be relied upon by Dr Martin as a basis for the opinions expressed in his report. While it is necessary to consider the specific objections made by the State below, it is convenient to address certain disputed matters of principle at the outset. On this topic, the State advanced three primary contentions.
45 First, the State contended that it is not permissible for an expert to base his or her opinion on the opinion of another person, in the sense of adopting and restating the opinion of another person. The State argued that an opinion formed in that manner is not an opinion within the meaning of the Evidence Act, being an inference drawn from facts (referring to Harrington-Smith at [40] per Lindgren J and Allstate Life Insurance Co v Australia & New Zealand Banking Group Ltd (No 5) (1996) 64 FCR 73 at 75 per Lindgren J); nor does it involve the application by the expert of his or her specialised knowledge to the relevant facts or assumptions underpinning the opinion of others, as required by s 79(1). I accept the contention as far as it goes. In general, the mere adoption and restatement of an opinion does not involve the application by the expert of his or her specialised knowledge and therefore cannot satisfy s 79.
46 A different question arises, though, when an expert relies on an opinion of another (qualified) person about a particular issue in forming an opinion about a dependent or related issue. The State acknowledged that it is permissible for an expert to rely upon reputable articles, publications and material produced by others in the area in which those others have expertise. In that regard, the State referred to the decision of Borowski v Quayle [1966] VR 382 (Borowski) in which Gowans J cited (at 386-387) the following passages from Wigmore on Evidence (3rd ed) Vol 2 at 784-785, para 665(b):
The data of every science are enormous in scope and variety. No one professional man can know from personal observation more than a minute fraction of the data which he must every day treat as working truths. Hence a reliance on the reported data of fellow scientists, learned by perusing their reports in books and journals. The law must and does accept this kind of knowledge from scientific men. On the one hand, a mere layman, who comes to Court and alleges a fact which he has learned only by reading a medical or a mathematical book, cannot be heard. But, on the other hand, to reject a professional physician or mathematician because the fact or some facts to which he testifies are known to him only upon the authority of others would be to ignore the accepted methods of professional work and to insist on finical and impossible standards. Yet it is not easy to express in usable form that element of professional competency which distinguishes the latter case from the former. In general, the considerations which define the latter are (a) a professional experience, giving the witness a knowledge of the trustworthy authorities and the proper source of information, (b) an extent of personal observation in the general subject, enabling him to estimate the general plausibility, or probability of soundness, of the views expressed, and (c) the impossibility of obtaining information on the particular technical detail except through reported data in part or entirely. The true solution must be to trust the discretion of the trial judge, exercised in the light of the nature of the subject and the witness' equipments. The decisions show in general a liberal attitude in receiving technical testimony based on professional reading.
47 The State acknowledged that Borowski has been considered in the context of anthropological evidence in a native title context in each of Jango No 2, Bodney and Yindjibarndi to permit reliance, by an anthropological witness, on writings of other anthropologists. The State submitted, however, that in each of those cases the expert witness relied on the writings of other anthropologists to provide the facts or assumptions on which the expert then based his or her opinion. The State contended that an opinion or conclusion of another cannot be an acceptable basis for an expert opinion. I will refer to that as the State's second contention.
48 In so far as the State's second contention sought to define a rule or principle governing the admissibility of expert opinion evidence, I reject it. There are numerous difficulties with any such rule or principle, not least of which it is not supported by authority. The distinction sought to be drawn by the State between facts and opinion, as a permissible basis for another opinion, is unsound. As is made clear by s 76 of the Evidence Act, an opinion concerns the existence of a fact. As recognised in the passage from Wigmore cited in Borowski, the state of knowledge in specialist fields at any point in time is often built upon a vast quantity of information that has been the subject of research or experimentation over long periods of time. A specialist in a field is not expected to know such information from personal observation. A specialist is entitled to use his or her judgment and rely upon opinions expressed by other qualified persons within the field, without interrogating the information relied upon by such other persons. In the context of anthropological evidence, submissions of the kind advanced by the State were rejected in each of Jango No 2, Bodney and Yindjibarndi. It is relevant to refer to each of those cases.
49 In Jango No 2, Sackville J considered an objection to anthropological evidence that relied upon opinions expressed in an unpublished anthropological report prepared by Dr Munn in 1965 from field work undertaken in 1964 to 1965. Justice Sackville observed (at [73]):
If an expert can express an opinion only if it is based on knowledge or information which is itself independently proved, serious practical difficulties are likely to arise. Thus in English Exporters (London) Ltd v Eldonwall Ltd [1973] Ch 415, Megarry J (at 420) made the following observations about an expert valuer's opinion:
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 more general and indefinite, will all have contributed their share. Doubtless much, or most, of this will be accurate, though some will not; and even what is accurate so far as it goes may be incomplete, in that nothing may have been said of some special element which affects values. Nevertheless, the opinion that the expert expresses is none the worse because it is in part derived from the matters of which he could give no direct evidence. Even if some of the extraneous information which he acquires in this way is inaccurate or incomplete, the errors and omissions will often tend to cancel each other out; and the valuer, after all, is an expert in this field, so that the less reliable the knowledge that he has about the details of some reported transaction, the more his experience will tell them that he should be ready to make some discount from the weight that he gives it in contributing to his overall sense of values.
50 Justice Sackville concluded (at [75]) that the research work of Dr Munn, in so far as it provided the basis, or one of the bases, for the opinions expressed in the anthropological evidence, was relevant and, subject to the operation of ss 135 and 136 of the Evidence Act, admissible in evidence. However, his Honour was not satisfied that Dr Munn's work did in fact form the foundation for any opinion in the anthropological evidence, and therefore the foundation for admissibility was absent (at [76]).
51 In Bodney, the Full Court concluded that the trial judge erred in disregarding anthropological evidence because it relied upon opinions expressed by another anthropologist, Prof Berndt, written in the 1970s with respect to the question whether the Noongar people had lost their traditions (at [84]-[95]). In a passage cited earlier, the Full Court confirmed that it is well established that experts are entitled to rely upon material produced by others in the area in which they have expertise as a basis for their opinions (at [92]).
52 Similarly, in Yindjibarndi, Rares J considered an objection to anthropological evidence which made reference to an earlier report prepared by other anthropologists for the purposes of satisfying the State (among others) about the applicant's assertions as to connection to the land and waters the subject of the proceedings. His Honour refused the objection and said that the earlier report, on which the expert witness had relied, was admissible as material produced by others in the area in which those other experts and the expert witness had expertise (at [6]).
53 As stated earlier, the rule for admissibility of opinion evidence is stated in s 79: the witness who gives the evidence must have specialised knowledge based on the person's training, study or experience and the opinion expressed in the evidence by the witness must be wholly or substantially based on that knowledge. While I do not accept the rule or principle propounded by the State with respect to reliance on the opinions of others, an expert witness must nevertheless demonstrate that his or her opinions are wholly or substantially based on the witness' training, study or experience. There may be circumstances in which the "mere" adoption of an opinion of another person does not satisfy the requirements of s 79, where the expert witness fails to demonstrate how the opinion of the witness is based on his or her training, study or experience.
54 The third contention advanced by the State is that qualifications to the hearsay rule, such as s 60, relax the restrictions on the admissibility of hearsay evidence, but do not relax other exclusionary rules such as the rules concerning opinion evidence in ss 76 to 79. The State argued that it is not permissible for an expert witness to rely on (hearsay) opinions expressed by others where those other opinions would not be admissible under s 79 of the Evidence Act. In support of that argument, the State relied on the High Court's decision in Lithgow City Council v Jackson (2011) 244 CLR 352 where it was held that ss 76 to 79 of the Evidence Act apply not only to evidence of opinions given by witnesses in court, but also to hearsay evidence (which may be admissible by way of exception to the hearsay rule, such as in the case of business records) (at [18] to [22] per French CJ, Heydon and Bell JJ, with whom Gummow and Crennan JJ agreed at [77] and [83] respectively).
55 The State did not refer to any decided case in which its third contention had been considered. The contention sits uncomfortably with the common law approach to expert opinion evidence, described in cases such as Borowski and English Exporters (London) Ltd v Eldonwall Ltd [1973] Ch 415, which allowed expert opinion to be based on reputable articles, publications and material produced by others in the relevant area of expertise. The contention also sits uncomfortably with the cases decided under the Evidence Act. I reject the contention for the following reasons.
56 As discussed by Lindgren J in Alphapharm Pty Ltd v H Lundbeck A/S [2008] FCA 559; 76 IPR 618 at [765]-[766], the extrinsic materials (the Australian Law Reform Commission's Interim Report on Evidence (ALRC No 26, 1985, Vol 1) at [685]) show that s 60 was introduced to enable hearsay evidence that is admissible for a non-hearsay purpose to be used by the court as evidence of the facts asserted by the evidence. This was expressly intended to apply to evidence forming the basis of an opinion. In that case, Lindgren J addressed objections to an expert report of a psychiatrist, Prof Montgomery. In his report, Prof Montgomery expressed opinions with respect to the therapeutic effects of a particular compound, and did so in reliance upon numerous published studies of the compound conducted by others. In considering an objection to Prof Montgomery's evidence by reason of his reliance on studies conducted by others (who were not to be called as witnesses in the proceeding), Lindgren J observed (at [770]):
Sections 59 and 60 are perhaps an odd way of grappling with the present issue. It seems clear, however, that it was intended that in a case like the present one, statements of the bases for expert opinions like those made by Professor Montgomery were to be characterised as being relevant for a purpose other than proof of the facts intended to be asserted by the representations by the authors of the articles. Prior to the enactment of s 60, the summaries given by Professor Montgomery of the effect of the journal articles would have been ruled admissible as falling within the exceptions dictated by necessity referred to at [761]-[765] above.
57 While s 60 provides an exception to the hearsay exclusionary rule, s 77 provides the same exception to the opinion exclusionary rule. Relevantly, ss 76 and 77 provide as follows:
76 The opinion rule
(1) Evidence of an opinion is not admissible to prove the existence of a fact about the existence of which the opinion was expressed.
(2) …
77 Exception: evidence relevant otherwise than as opinion evidence
The opinion rule does not apply to evidence of an opinion that is admitted because it is relevant for a purpose other than proof of the existence of a fact about the existence of which the opinion was expressed.
58 In my view, the cases referred to above show that, if the opinion of an expert witness in a proceeding is based upon opinions expressed in publications and material produced by others, those other opinions are admissible to prove the foundation of the expert witness' opinion. As such, the other opinions are admissible under s 77 "for a purpose other than proof of the existence of a fact about the existence of which the opinion was expressed" in the same manner as they are admissible under s 60. Once admitted, they may be relied on for all purposes.