Decision-makers' dilemma: evaluating expert evidence

• Jurisdiction: South Africa
• Citation: (2000) 13 SACJ 319
• Published date: 24 May 2019
• Date: 24 May 2019
• Author: Lirieka Meintjes-van der Walt
• Pages: 319-343

Decision-makers' Dilemma:

Evaluating Expert Evidence

LIRIEKA MEINTJES-VAN DER WALT*

The normative question of how expert knowledge is best assessed, and

how experts themselves are best evaluated and kept under a modicum of

control, raises such intractable and viciously circular problems as to

strangle speech

Barnes and Edge (eds)

Science in Context

(1982) 33

1 Introduction

The ascertainment of facts, based on proof, is not unique to the legal

process.

1

While finding facts in law involves the same logic as scientific fact-

finding, the difference between legal fact-finding and law-constructing

procedures are justified by law's response to the social and normative order

rather than the natural order.

2

Proof

3

in both science and law,

4

is a quantum

and quality of evidence or data sufficient to support a conclusion. Loevinger

concludes that '[p]roof ultimately depends on the ability of the human mind

to make appropriate and useful distinctions and connections among data or

items of evidence'.

5

Fact-finders, in the context of expert evidence, are not

only faced with the task of determining which elements of expert evidence

must be disregarded as irrelevant or unimportant, but must also find means

of determining the significance or weight that should be attached to expert

evidence in any given case.

* B Juris LLB (UPE) LLM (Rhodes),

Senior Lecturer in Law, Rhodes University.

1

L Loevinger 'Standards of Proof in Science and Law' 1992 32

Jurimetrics Journal 323.

2

DH Kaye 'Proof in Law and Science' 1992 32

Jurimetrics Journal 313,

321.

3

The

Oxford English Dictionary

defines proof as 'that which makes good or proves a statement;

evidence sufficient (or contributing) to establish a fact or produce belief in the certainly

of something'.

Webster's Third International Dictionary

defines proof as the cogency of

evidence or of demonstrated relationship that compels acceptance by the mind of a truth or

fact'.

4

The difference between the standards of proof in law and the so-called 'hard' sciences lies in

the nature and measurement of the proof acceptable to the discipline. Evidence that lawyers

rely on as means of proof are usually in the form of an account by witnesses expressed in

verbal terms, while data produced by the usual techniques of the 'hard sciences', measuring

and counting, is usually expressed numerically.

5

L Loevinger (op cit n 1).

319

(2000) 13 SACJ 319

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320

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SACJ • (2000) 13 • SAS

The philosopher Coady reflects on the dilemma that confronts legal

decision-makers faced with expert evidence. The legal tribunal must decide

'at least three questions:

(a)

whether the witness is indeed expert in the field;

(b)

whether the field is a genuine area of science;

(c)

whether, given a positive answer to

(a)

and

(b),

his particular

depositions are credible. All three of these questions pose difficulty

for a legal tribunal since they seem to be questions that only an expert

can answer.'

7

The ratio for the introduction of expert evidence is the possibility that it could

assist the trier of fact on deciding the issues at stake

s

Even though the

tribunal of fact is not bound by the views offered by the expert,

9

the dilemma

is, who is to assist the trier of fact in evaluating this very evidence which has

been introduced to assist it? In the context of adversarial litigation, the

additional problem associated with the assessment of conflicting expert

evidence, prompted Hand to conclude: '[The jury] will do no better with the

so-called testimony of experts than without, except where it is unanimous. If

the jury must decide between [conflicting experts] they are as badly off as

if they had none to help them.'

10

The dilemma of conflicting expert opinions

has in South Africa resulted in courts being unable to rely on expert

evidence." This problem is overcome in some inquisitorial systems where

6

CAJ Coady

Testimony: Philosophical Study (1992).

7

Ibid 291.

8

S v Van As

1991 2 SACR 74 (W) 86c—e. See also generally FE Raitt 'A New Criterion for the

Admissibility of Scientific Evidence: The Metamorphosis of Helpfulness' in H Reece (ed)

Law

and Science Current Legal Issues

(1998) 153.

9

In

Davie v Magistrates of Edinburgh

[1953] SC 34 the

locus classicus

on the fact that a judge or

jury is not bound by the views of an expert, Lord President Cooper held: 'Expert witnesses,

however skilled or eminent, can give no more than evidence. They cannot usurp the function

of the jury or Judge sitting as a jury, any more than a technical assessor can substitute his

advice for the judgment of the court. Their duty is to furnish the Judge or jury with the

necessary scientific criteria for testing the accuracy of their condusions so as to enable

the application of their criteria to the facts proved in evidence. The scientific opinion, if

intelligible, convincing and tested becomes a factor (and often an important factor) for

consideration along with the whole other evidence in the case, but the decision is for the

Judge and jury.' However, Kriegler J in

S v M

1991 SACR 91 CO emphasised the fact that

the wise judicial officer does not lightly reject expert evidence on matters falling within the

purview of the expert witness's field. . . . One does not reject such evidence readily where

the expert has furnished his opinions — and the foundational reasons therefore in a

satisfactory manner' (99h-100

c).

10

L Hand 'Historical and Practical Considerations Regarding Expert Testimony' (1901-02) 15

Harvard Law Review

40 56.

11

See

S v Calitz

1990 1 SACR 119 (A) per Eksteen AJ: Waar die hof met twee botsende

psigiatriese menings te make het, kan dit kwalik van die Hof verwag word om die een bo die

ander te verkies. Op stuk van sake is die Hof 'n leek op die gebied van psigiatrie, en kan hom

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