Opinion Evidence and Experts
SYLLABUS REFERENCE
19. Opinion evidence and experts
The general prohibition on the use of opinion evidence in criminal cases,
The exception to this rule in relation to expert evidence,
The definition of an expert,
The scope and limits of expert evidence in the trial,
The procedural requirements for the introduction of expert evidence under the
Criminal Procedure Rules.
READING:
Required Reading
CLS Evidence Manual 2014, Chapter
Opinion Evidence
General rule
In civil and criminal cases, the opinions of witnesses are not generally admissible
Opinions and conclusions are for the court to reach, based upon information
placed before it
The general rule is subject to two important exceptions where the court lacks
the witness’s competence to form an opinion on a particular issue:
o Lack of the necessary direct knowledge
o Lack of the necessary expertise
Witnesses of fact who offer their opinion
Statements of opinion by an eyewitness to the facts in issue are often really a
convenient way of stating several facts
o Such as the defendant was drunk
Such a statement will generally be admissible as long as a proper appraisal of the
facts does not call for any special expertise
If a degree of precision is required, then a witness’s best guess or estimate by
itself will probably not do
Expert opinion evidence
General principle
The opinion of an expert is admissible
If an issue calls for expert evidence, the evidence of a non-expert should not be
admitted
The line between matter that do call for expert evidence and matters that do not
is often extremely fine (especially in relation to psychiatric evidence) and the
courts consider the question most carefully
1
, Expert evidence will usually be excluded if it merely offers an opinion on normal
human behaviour
o The question is what is normal behaviour?
In a development from the position in R v Turner, expert evidence may now be
called not merely where the accused is alleged to be suffering from a recognised
mental illness, but also if it could show that the accused is suffering from a
personality disorder that would tend to affect the reliability of the confession or
other evidence
It is an objective test – the ‘reasonable man’ cannot be assumed to be abnormal.
In so far as an expert’s evidence would only be relevant if such an assumption
could be made then it would appear to be inadmissible
It should be noted that evidence of fact must not be confused with expert
evidence, even where it is given by a witness whose qualifications would entitle
that witness to give expert evidence
There is no statutory equivalent of the Civil Evidence Act 1972 to permit experts
in criminal cases to offer their opinions on ultimate issues but it seems to be a
matter of the form that questions take now, rather than their substance
Who is an expert?
Only a suitably qualified expert can give expert evidence
But this does not mean that there must be formal qualifications
o See CLS Manual 17.3.2 for examples
It ought to be clear that the expert owes an overriding duty to the court, not to
himself or to a litigant (Crim PR, r 33.2)
Potential conflict of interest
A litigant who wishes to call an expert as a witness should disclose to the other
litigant(s) and the court any interest that the expert has, or may seem to have in
the proceedings
There is also an obligation on the expert to disclose any potential conflict of
interest; this may be done by attaching the expert’s curriculum vitae to the
report
That interest will not automatically disqualify the expert, although
disqualification may be required on the facts of the particular case
It has been said that it is ‘the nature and extent of the interest or connection which
matters, not the mere fact of the interest or connection’
Apparent bias is not enough to disqualify an expert from being called as a
witness
o The key questions are:
Does the person have relevant expertise?
Is he aware of the overriding duty as an expert to the court, and
willing and able to fulfil it?
2
SYLLABUS REFERENCE
19. Opinion evidence and experts
The general prohibition on the use of opinion evidence in criminal cases,
The exception to this rule in relation to expert evidence,
The definition of an expert,
The scope and limits of expert evidence in the trial,
The procedural requirements for the introduction of expert evidence under the
Criminal Procedure Rules.
READING:
Required Reading
CLS Evidence Manual 2014, Chapter
Opinion Evidence
General rule
In civil and criminal cases, the opinions of witnesses are not generally admissible
Opinions and conclusions are for the court to reach, based upon information
placed before it
The general rule is subject to two important exceptions where the court lacks
the witness’s competence to form an opinion on a particular issue:
o Lack of the necessary direct knowledge
o Lack of the necessary expertise
Witnesses of fact who offer their opinion
Statements of opinion by an eyewitness to the facts in issue are often really a
convenient way of stating several facts
o Such as the defendant was drunk
Such a statement will generally be admissible as long as a proper appraisal of the
facts does not call for any special expertise
If a degree of precision is required, then a witness’s best guess or estimate by
itself will probably not do
Expert opinion evidence
General principle
The opinion of an expert is admissible
If an issue calls for expert evidence, the evidence of a non-expert should not be
admitted
The line between matter that do call for expert evidence and matters that do not
is often extremely fine (especially in relation to psychiatric evidence) and the
courts consider the question most carefully
1
, Expert evidence will usually be excluded if it merely offers an opinion on normal
human behaviour
o The question is what is normal behaviour?
In a development from the position in R v Turner, expert evidence may now be
called not merely where the accused is alleged to be suffering from a recognised
mental illness, but also if it could show that the accused is suffering from a
personality disorder that would tend to affect the reliability of the confession or
other evidence
It is an objective test – the ‘reasonable man’ cannot be assumed to be abnormal.
In so far as an expert’s evidence would only be relevant if such an assumption
could be made then it would appear to be inadmissible
It should be noted that evidence of fact must not be confused with expert
evidence, even where it is given by a witness whose qualifications would entitle
that witness to give expert evidence
There is no statutory equivalent of the Civil Evidence Act 1972 to permit experts
in criminal cases to offer their opinions on ultimate issues but it seems to be a
matter of the form that questions take now, rather than their substance
Who is an expert?
Only a suitably qualified expert can give expert evidence
But this does not mean that there must be formal qualifications
o See CLS Manual 17.3.2 for examples
It ought to be clear that the expert owes an overriding duty to the court, not to
himself or to a litigant (Crim PR, r 33.2)
Potential conflict of interest
A litigant who wishes to call an expert as a witness should disclose to the other
litigant(s) and the court any interest that the expert has, or may seem to have in
the proceedings
There is also an obligation on the expert to disclose any potential conflict of
interest; this may be done by attaching the expert’s curriculum vitae to the
report
That interest will not automatically disqualify the expert, although
disqualification may be required on the facts of the particular case
It has been said that it is ‘the nature and extent of the interest or connection which
matters, not the mere fact of the interest or connection’
Apparent bias is not enough to disqualify an expert from being called as a
witness
o The key questions are:
Does the person have relevant expertise?
Is he aware of the overriding duty as an expert to the court, and
willing and able to fulfil it?
2
