ADMISSIBILITY OF EXPERT OPINION EVIDENCE
Martin L. Sides Q.C.
Acting Senior Public Defender
NSW
Introduction
For the purpose of this paper, it is acceptable to define the word "opinion" in the
traditional way: "an inference from observed and communicable data" or facts
(Australian Law Reform Commission Report 26, para 156; Cross - para 15.3).
It is generally accepted that a witness is only permitted to speak of what he or she directly
observes through the use of the five senses. The drawing of inferences is the function of the
tribunal of fact. It is not the business of witness' to draw inferences or express opinions, a
witness' function is to state facts.
The dividing line between "fact" and "opinion" is far from clear and the above rules are
not necessarily easy in their application. For the purposes of this paper, it is unnecessary
to explore those murky waters because there is a well established exception that permits an
"expert witness" to give opinion evidence. Before such an opinion is admissible, three
things need to be established:
(i)
the field of expertise;
(ii)
the witness is a qualified expert; and
(iii)
the matter to which the material relates is not within ordinary human
experience - "common knowledge".
The decision of the High Court in Clark v Ryan (1960) 130 CLR 486 has become a
touchstone for the principles in this area of the law. In that case Dixon, CJ (with whom
Fullager, J agreed) said:
"The rule of evidence relating to the admissibility of expert testimony as it effects
the case cannot be put better than it was by J. W. Smith in the notes to Carter v
Boehm, 1 Smith L.C., 7th ed. (1876) p 577. "On the one hand" that author wrote,
"it appears to be admitted that the opinion of witnesses possessing peculiar skill
is admissible whenever the subject matter of enquiry is such that inexperienced
persons are unlikely to prove capable of forming a correct judgment upon it
without such assistance, in other words, when it so far partakes of the nature of
a science as to require a course of previous habit or study, in order to the
attainment of a knowledge of it." Then after the citation of authority the author
proceeds: "While on the other hand, it does not seem to be contended that the
opinion of witnesses can be received when the enquiry is into a subject matter
the nature of which it is not such as to require any peculiar habits or study in
order to qualify a man to understand it." Adapted by Harding A.C.J. in R v
Camm (1883) 1 Q.L.J. 136.
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In R v Parker [1912] VLR 153, one of the cases establishing the evidentary use of
fingerprints to prove identity, Cussen, J. in that connection said that expert
witnesses may give in evidence statements based on their own experience or study
but that they cannot be permitted to attempt to point out to the jury matters which the
jury could determine for themselves or to formulate their empirical knowledge as a
universal law. To this should be added the observation made by Vaughan
Williams, J. during the argument of R v Silverlock [1894] 2 Q.B. 766, viz. "no one
should be allowed to give evidence as an expert unless his profession or cause of
study gives him more opportunity of judging than other people" (At p 769). The
words "profession or course of study" have of course a wide meaning and
application: see per Lord Russell, CJ. (at 771)."
General rules of admissibility also apply. For example, the expert's opinion must be
relevant to a matter in issue. If the prejudicial effect outweighs the probative value the
judge has a discretion to exclude the evidence: R v Elliott (unreported NSW SC 6 April
1990, Hunt, J); R
v
Tran (1990) 50 A.Crim.R. 233. If the expert, in drawing
inferences, enters into the field of mere speculation the opinion evidence would be
rejected: Straker v R (1977) ALR 103 (High Court of Australia).
Rules of Admissibility
The special rules applying to the admissibility of the opinion of expert witnesses have been
formulated as a result of a healthy scepticism on the part of judicial officers in relation to
"experts" who are essentially seen as biased because they are paid by the party calling
them. The ultimate decision in each case is for the tribunal of fact and courts have been
jealous to guard that territory. They do not like it being usurped by expert witnesses.
Another way of looking at that might be that an impressive expert may hold undue sway
with the tribunal of fact, particularly a jury.
Common Knowledge Rule
The Australian Law Reform Commission contends that there are 2 distinguishable
approaches to this exclusionary rule (report No 26, Para 158, 354):
(a)
The traditional approach - which excludes expert opinion which relates to
matter falling within ordinary human experience; and
(b)
The functional approach - the fact finding tribunal will be assisted by
evidence from an expert.
The traditional approach is inflexible and has led to absurdities. This is no better
exemplified than in the artificial approach by the courts allowing
psychologists/psychiatrists to give evidence in the case of abnormal people, but not normal
people: R v Turner [1975] 1 Q.B. 834, 841; R v McEndoo (1981) 5 A.Crim.R. 52, 55; R
v Ashcroft [1965] 1 Qd.R. 81, 85. It was taken to absurd lengths in R v Masih [1986]
Crim.L.R. 395.
The functional approach is more flexible and its application exposes the illogicality of the
traditional approach: R v Schultz (1985) 5 A.Crim.R. 234, 237); Murphy v The Queen
(1989) 167 CLR 94, 111, 125-127, 131; R v Runjanjic (1991) 53 A.Crim.R. 362.
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Is The Witness A Qualified Expert?
Before a court will admit evidence of an expert it must be satisfied that the witness has the
appropriate expertise. In Clark v Ryan some members of the High Court, Menzies and
Windeyer, JJ., said that this rule was not complied with unless the witness gained his
expertise from a course of study (see pp. 591-2). Dixon, CJ. and McTiernan, J. took the
view that the expertise could be gained from either a field of study or as a result of
practical experience (pp. 491-2, 498-99). A similar view has been taken in R v Silverlock
[1894] 2 Q.B. 766. The High Court, however, did not reach a consensus on this point as
Fullager, J. agreed with both the Chief Justice and Menzies J!
As a matter of practice however, the rule is applied as pronounced by Dixon, CJ. Hence
experts in fingerprinting, crime scene examination, ballistics, firearms and documents
examination have been permitted to give evidence when their expertise is gained not by
way of formalised courses but by process of experience acquired on the job
(Freckleton and Selby 1993 para 7.210).
Understanding that part of the principle is easy, but there is little guidance as to how to
apply it in practice:
"In such a matter, it seems to me, that there are no precise rules. The court is
expected to rule on the qualifications of an expert witness, relying partly on what
the expert himself explains, and partly on what is assumed, though seldom
expressed, namely that there exists a general framework of discourse in which it is
possible for the court, the expert and all men according to their degrees of
education, to understand each other. Ex hypothesis this does not extend to the
interior scope of the subject which the expert professes. But it is assumed that the
judge can sufficiently grasp the nature of the expert's field of knowledge,
relate it to his own general knowledge, and thus decide whether the expert has
sufficient experience of a particular matter to make his evidence admissible. The
process involves an exercise of personal judgment on the part of the judge, for
which authority provides little help" (Blackburn, J. in Milirrpum v Nabalco Pty.
Ltd. (1971) 17 FLR 141, 160).
Once in the witness box the expert must be limited to giving evidence within the scope of
his or her expertise. Thus a GP would not be qualified to give an opinion that lies in the
specialty of a neurologist. A psychologist is not qualified to diagnose mental illness: R v
MacKeenney (1983) 76 Cr.App.R. 271; R v Pesisley (1990) 54 A.Crim.R. 42, 52; R v
Ford (1986) 19 A.Crim.R 1; Klimoskiv v Water Authority of W.A. (1989) 5 SASR 148,
150.
Field Of Expertise
It is now accepted that an opinion of an expert witness will not be admitted as evidence
unless that evidence relates to a field of expertise. How is a judge to determine what is a
field of expertise? It has been contended that courts in Australia, Britain and Canada have
not definitively set out the criteria to the employed in applying this rule (Freckelton
and Selby 1993 para 9.10).
Clearly an organised branch of knowledge which is identifiable as a discipline in the
social or physical science would qualify (Gillies 1986 p. 601; Menzies, J. in Clark v Ryan
at 501). As Gillies notes on the one hand, such a definition is too narrow given that human
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skill is constantly evolving. On the other hand opinion evidence cannot be something
which is part of every day experience, the common knowledge rule.
"In these terms expertise for the purposes of the opinion rule may be characterised
broadly as consisting of a body of knowledge and/or skills based upon experience
or training which concerns a subject which is of such a nature that it can be grasped
and commented upon in an informed way by a person with training and/or
experience extending beyond that possessed by the average person (Gillies 1986 p.
602).
This can be regarded as a useful definition of this rule. Because, broadly speaking, it
encompasses the decisions (at least in Australia) dealing with this aspect.
In the USA the "Frye test" is commonly but not universally regarded as laying down the
criteria for accepting or rejecting new scientific techniques. Frye v United States is a
decision of the Court of Appeal of the District of Columbia relating to polygraph testing:
"Just when a scientific principle or discovery crosses the line between the
experimental and demonstrable stages is difficult to define. Somewhere in this
twilight zone the evidential force of the principle must be recognised, and while
courts will go a long way in admitting expert testimony deduced from a well
recognised scientific principle or discovery, the thing from which the deduction is
made must be sufficiently established to have gained general acceptance in the
particular field in which it belongs" (297 F 1013 at 1014).
One could spend a day examining judgments of courts here in an attempt to ascertain
whether the "Frye test" has been endorsed in Australia (for analysis see Freckelton and
Selby 1993 paras 9.10-9.180; Freckelton 1989 pp 10-15). Maurice, J in R v Lewis
(1987) 29 A.Crim.R. 267, 271 regarded the "Frye test" as a useful guide but, said that the
Crown had to demonstrate that evidence of a novel kind is scientifically reliable (p. 271).
It can be legitimately argued that the test laid down in R v Gilmore [1977] 2 NSWLR 935,
939 also refers to criteria to be used in the application of this rule. In that case the court
said that not all scientific techniques could be the subject of expert testimony. The court
said that the following criteria should be considered:
(a)
Undue weight can be attached to so called objective opinion;
(b)
it can be difficult to refute expert testimony;
(c)
whether there is a demonstrably objective procedure to reach the opinion;
and
(d)
whether there are other qualified persons who can duplicate the results of
any testing employed by the expert.
This criteria was used in R v McHardie [1983] 2 NSWLR 733, 753. Interestingly those
criteria were taken from a decision of the US Court of Appeals: US v Ballen (1975) 519
Fed. 2d 463, 466-7. It has also been applied in South Australia: R v Bonython (1984) 15
SASR 364, 366 and Victoria R v Lucas [1992] 2 VR 109.
A further criteria could be added to that list:
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(e)
Whether there are means by which the tribunal of fact can be assured of
correctness of the opinion.
As to sub-paragraph (a)
McInerney in R v Tran said:
"Forensic evidence, especially if it goes to the vital issue implicating an accused
person in the commission of an offence, may often have a prejudicial effect on the
mind of a jury which far out ways its probative value. The jury, being people
without scientific training may often be impressed with an expert's qualifications,
appointments and expertise and the confident manner in which he expresses his
opinion. And yet it ought not be left to such matters alone to provide a foundation
for the jury making an assessment of the probative value of forensic evidence,
particularly where there are conflicts in expert testimony, or where it is
acknowledge that other experts of more or less equal distinction are unlikely to
agree" (p. 242).
See also Muirehead, AJ in Lewis at p 288; Madden, CJ. in R v Parker [1912] VLR 152
spoke about the dangers in fingerprint type evidence because of its "savour of mystery".
The absence (Tran) or presence (Elliott) of corroboration will reflect on the weight of the
evidence, and hence is a relevant factor to admissibility.
As to sub-paragraph (b)
It sometimes occurs that an expert has examined physical objects which have been
subsequently destroyed. Sometimes photographs of those objects may have been taken
which are less then satisfactory. This can place the expert in a position of advantage and
may result in undue weight being given to his or her evidence. The calling of an expert
places a tactical burden on the other party to call an expert. It is often difficult to refute an
opinion via cross-examination.
As to sub-paragraph (c)
The tribunal of fact has to form an independent judgment and not just adopt the expert's
view: ULV Pty Ltd v Scott (1990) 19 NSWLR 190. Hence the tribunal of fact must be
given the basis for that independent assessment: R v Tran (p. 237).
As to sup-paragraph (d)
This leads to the need for more than one expert in the given field.
As to sub-paragraph (e)
The tribunal of fact (which is usually a jury in criminal cases) is charged with the function
of determining which of the competing opinions it can act on. Some times this is too
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difficult for the jury, as was acknowledge by Gibb, CJ and Mason, J in Chamberlain v
The Queen (1983-84) 153 CLR 521, 558 (where their Honours' quoted with approval from
Jenkinson, J in the court below (1983) 72 FLR 1 at 81-82). Dixon, CJ had noted in Clarke
v Ryan that juries might find technical evidence unintelligible (491). This was the basis
for the rejection of DNA evidence in R v Tran (242-243) and R v Lucas [1992] 2 VR
109 at 118 (per Hampel, J VIC. SC). It is quite a different basis for the rejection of
evidence than the exercise of the overriding discretion to reject it where it is highly
prejudicial and of little probative weight. In R v Lewis Maurice, J emphasised the need
for the Crown to lead evidence in a way that puts jurors in the proper position to make an
evaluation of the experts (p. 271).
The Queensland Court of Criminal Appeal in R v Carroll (1985) 19 A.Crim.R. 410
allowed an appeal because "expert" odontology evidence did not assist the jury in the
process of deciding which witness to accept (p. 417, 435). Yet in remarks which were
obiter dicta, the court set out criteria of admissibility using terminology very similar to the
"Frye test".
Other Bases For Exclusion
Even where "expert evidence" passes muster on the above rules it may stumble upon other
rules which have general application beyond this area of the law: some of these are
discussed below:
(a) Matter In Issue
It has been said that an expert will not be able to express an opinion concerning the
ultimate matter in issue: R v Darrington [1980] VR 353. However in Arnotts Pty Ltd v
T.P.C. (1990) 97 ALR 555 it was said the expert could do this as long as such expert
identifies the facts assumed in arriving at that opinion. Hence in cases of insanity,
diminished responsibility and fitness to plead, psychiatrists express an opinion on the
ultimate issue. (See also R v Fowler (1985) 39 SASR 440, 443; Phipson 13ed para 561,
12ed para 1210). There is a danger if the expert expresses an opinion on a matter in issue:
that opinion might become the focus of attention and have the potential to mislead and
prevent jurors from analysing and understanding other observations made and opinions
expressed by the expert: R v Chayna (unreported, NSW CCA, 15.2.93) pp. 21-22.
(b)
Facts Proved
A court will not act on the opinion of the expert unless the facts upon which the opinion is
based are proved in evidence: Paric v John Holland Constructions (1985) 62 ALR 85,
87-88; [1984] 2 NSWLR 505; Arnotts v TPC at 591.
An expert may draw on hearsay material in predicting the likelihood of an event so long as
that material is disclosed: R v Abadon [1983] 1 All.E.R. 364. However the witness must
have some expertise in the mathematical/statistical material relied upon:
"In our view, if the fact that the method of mathematical analysis employed
(including the use of the computer) in some way went outside the field of specialist
knowledge which Mr Jones had, and gave out results upon which he acted in
coming to his final conclusion, so that it could be said that conclusion did not arise
from his expertise, then his evidence should not have been admitted" (McHardie at
p 754; see also R v Lucas [1992] 2 VR 109, 114).
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(c)
Reliability
If scientific testing in the particular case is unreliable or, produces misleading and
confusing impressions it my be rejected: R v Elliott; R v Tran (242), even though
generally such tests produce acceptable and admissible results.
(d)
Demonstrations/Reconstructions
A court may receive evidence of demonstrations conducted in its presence: Scott v The
President & Counsellors & Rate Payers of the Shire of Numurkah (1954) 91 CLR 300.
In criminal trials evidence will be admitted of test experiments or reconstructions of
crimes undertaken and the results thereof. Such evidence will be admitted if
(a)
The evidence would enlighten the jury and enable them to more intelligently
consider the issues;
(b)
The experiment should be under circumstances similar to those prevailing at
the time of the occurrence. They do not need to be identical but should be
reasonably or substantially similar: R v Ireland (No. 2) [1971] SASR 6
(SA Supreme Court Full Court); R v Thompson (1986) 23 A.Crim.R. 340;
R v Brady (unreported, NSW SC, 7 April 1989 per Campbell, J.);
Wigmore (p 436).
Such reconstructions can be undertaken either by lay persons or experts R v Ireland (at p
14); R v Thompson (p 346-7). Those cases do not lay down the criteria to be applied in
determining whether or not an expert should have undertaken the experiment before it will
be admitted. Campbell, J. said in Brady the criteria to be applied was the same as that
applied in determining whether to admit expert opinion evidence: namely whether there is
a recognised field of study relating to the particular subject matter and whether that subject
matter is outside common experience (p. 5-6).
References
Australian Law Reform Commission, Report No. 26 Interim, `Evidence' Vol. 1.
Byrene, D. & Hayden `Cross on Evidence' 3rd Aust Ed.
Freckleton, Ian 1989, `DNA Profiling: Forensic Science Under the Microscope' - paper
delivered at Australian Institute of Criminology Conference - DNA and Criminal
Justice - Canberra 30-31 October 1989.
Doyle, J. Features on the Anglo-American System of Evidence in Trials at Common Law
3rd ed (1940) Vol. 2.
Gillies `Opinion Evidence' 1986, 60 ALJ 597.
Phipson `The Law of Evidence' 12th ed.
Glass 1975, `Seminars on Evidence'.
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