Admissibility of expert opinion evidence Flashcards
Admissibility of expert opinion evidence
Where a matter calls for special skill or expertise, only a witness who is an expert in the matter can give evidence, and the range of opinion evidence is limited to matters where the opinion is needed in order to illuminate the facts in the case.
This means that if facts can be stated without reference to an
opinion, the expert is not allowed to express an opinion on the matter.
Section 25 governs the admissibility of expert opinion evidence:
25 Admissibility of expert opinion evidence
(1) An opinion by an expert that is part of expert evidence offered in a proceeding is admissible if the fact-finder is likely to obtain substantial help from the opinion in understanding other evidence in the proceeding or in ascertaining any fact that is of
consequence to the determination of the proceeding.
(2) An opinion by an expert is not inadmissible simply because it is about—
(a) an ultimate issue to be determined in a proceeding; or
(b) a matter of common knowledge.
(3) If an opinion by an expert is based on a fact that is outside the general body of knowledge that makes up the expertise of the expert, the opinion may be relied on by the fact-finder only if that fact is or will be proved or judicially noticed in the proceeding.
(4) If expert evidence about the sanity of a person is based in whole or in part on a statement that the person made to the expert about the person’s state of mind, then—
(a) the statement of the person is admissible to establish the facts on which the expert’s opinion is based; and
(b) neither the hearsay rule nor the previous consistent statements rule applies to evidence of the statement made by the person.
(5) Subsection (3) is subject to subsection (4).
Section 25 is concerned only with the admissibility of expert opinion
evidence. Expert evidence may consist of fact, opinion, or a mixture of the two (s4). Factual evidence from an expert will be governed only by the general rules in ss7 and ss8, and any other admissibility rules applicable in the individual case.
If the evidence is opinion evidence, then in order to comply with s25, the opinion must
- be that of an “expert”
- comprise “expert evidence”, and
- offer substantial help to the fact-finder in understanding other evidence or ascertaining any fact in the proceeding.
Qualification as an expert
Section 4 of the Act defines an “expert” as “a person who has specialised knowledge or skill based on training, study or experience”. The judge must determine whether the expert witness is properly qualified to testify: opinions given by non-experts on matters calling for expertise are inadmissible.
The expert is required to demonstrate to the court that he or she has the requisite qualification to be deemed “expert” in the field in question; the expert may be qualified through formal study and training, from experience, or both. Evidence offered by an expert should be within his or her area of expertise.
“Likely to obtain substantial help”
Section 25(1) provides that expert opinion evidence will be admissible if the fact-finder is likely to obtain substantial help from the opinion in:
- understanding other evidence, or
- in ascertaining any fact that is of consequence in the determination of the proceeding.
“Substantial help” replaces the two defining common law rules that related to expert opinion evidence and are abolished in s25(2): the common knowledge and ultimate issue rules. The common knowledge rule stated that an expert could not give an opinion on matters that were within the common knowledge of the jury. The ultimate issue rule provided that an expert could not give an opinion on the ultimate issue in the case. The requirement of substantial helpfulness seeks to offer a “more rational test that assesses the reliability and value of the expert opinion on its merits”. The
Court in B v R25 held that it “necessitates consideration of an amalgam of relevance, reliability and probative value”.
Evidence based on proven facts
Opinion based on facts outside the general body of information will need to be proved or judicially noticed. In R v Turner26 the Court said that:
“Before a court can assess the value of an opinion it must know the facts upon which it is based. If the expert has been misinformed about the facts or has taken irrelevant ones into consideration or has omitted to consider relevant ones, the opinion is likely to be valueless. In our judgment, counsel calling an expert should in examination in chief ask his witness to state the facts upon which his opinion is based. It is wrong to leave the other side to elicit the
facts by cross-examination.”
The factual basis of an expert opinion needs to be proved as, without it, the opinion can be given little weight. Indeed, where there is no proven factual basis, the evidence may carry so little weight that it will not be relevant. Where current knowledge does not allow an opinion based on proven facts, then the expert should indicate that he or she cannot express a view.
- Where material, such as books and journal articles, contribute to the general body of information on any given topic, an expert witness is allowed to base his or her opinion partly on this information: to do
otherwise would involve a costly and time-consuming parade of experts in court. (For example, research on memory processes has been conducted by a large number of scientists, the results of which make up a body of knowledge, but no one scientist has personally conducted a sufficient number of experiments to be able to give a full breadth of comment on the basis of personal experience alone.) - An expert opinion may also be based on facts that are supplied by others, such as analyses of body tissues carried out by colleagues, or the research findings of other scientists. In this way, the facts on which an expert witness bases his or her opinion may be assumed facts, or facts of which they have no first-hand knowledge (for example, where there are marks on a body, a surgeon who has not seen the body may be asked whether, given the nature of the wounds, they could be self-inflicted). The expert should state the assumed facts on which the opinion is based, and the admissible evidence offered is the assumed facts themselves. If research findings were relayed directly to the court, rather than being used to
support and explain the conclusions reached by the expert witness, they would be hearsay evidence and may be excluded under s18.
Section 129 can act to allow published documents to be admitted as evidence where the Judge decides that they are reliable sources, without having to have recourse to the rules relating to opinion evidence. Where an expert has his or her evidence peer reviewed, this will be admissible provided that it meets the
requirements of s18 Evidence Act 2006.
Proven facts and provisional admissibility under s14
Section 25(3) requires that the fact “is or will be proved”. This means that the expert witness may either state the facts on which the opinion is based during evidence-in-chief, or give the evidence on the basis that it “will be” proven, ie that it is provisionally admissible (under s14 of the Evidence Act 2006). As it is a conditional process, admissibility in such cases will depend on whether the factual basis of the opinion is indeed proven. If the evidence proving the
factual basis does not eventuate, or if it is insufficient to establish the
admissibility of the expert opinion then the opinion will be disregarded. (In a jury trial, there will be a direction to rely on the expert opinion only if it finds the factual basis proven.)
Expert evidence about sanity
Section 25(4) provides for the admissibility of a person’s statement about his or her state of mind in order to establish the factual basis for the expert’s opinion on the sanity of that person. It limits its scope to opinions based on statements made by the person whose sanity is in issue, thereby excluding statements by others, or statements pertaining to mental disorders falling short of legal insanity. Furthermore, the statements must be about the person’s state
of mind, and so any statements informing the expert’s opinion made about other issues will not be covered by s25(4).
The conduct of experts
Expert witnesses should be impartial in their assistance to the court. In R v Hutton27, the Court of Appeal approved principles similar to those for experts in civil cases. These principles summarise much of the discussion of s25 above:
* an expert must state his or her qualifications when giving evidence
* the facts, matters and assumptions on which opinions are expressed must be stated explicitly
* the reasons for opinions given must be stated explicitly
* any literature or other material used or relied on to support opinions must be referred to by the expert
* the expert must not give opinion evidence outside his or her area of
expertise
* if an expert witness believes that his or her evidence might be incomplete
or inaccurate without some qualification, that qualification must be stated
* an expert has an overriding duty to assist the Court impartially on relevant matters within the expert’s area of expertise, and
* an expert is not an advocate for any party.
Notice Requirement
The Criminal Disclosure Act 2008 introduced an obligation on the defence to give notice of expert evidence in criminal proceedings. Section 23 provides that, if the defendant intends to call an expert witness, he or she must disclose the brief of evidence or report (or a summary if no brief or report is yet available) at least 14 days before the date fixed for the trial.
Summary
- The exclusive rules of evidence deal with:
− veracity
− propensity
− hearsay
− opinion
− identification
− improperly obtained evidence.
- The Evidence Act 2006 divides what was called “character” evidence at common law into two classes of evidence:
− “veracity” – a disposition to refrain from lying, and
− “propensity” – a tendency to act in a particular way.
- The two criteria for admissibility of hearsay are: reliability; and
unavailability or that “undue expense or delay would be caused”. - In criminal proceedings, a notice of hearsay must be served on the other party so that each party has sufficient time, prior to the proceeding, to respond to the statement.
- Opinion evidence is not generally accepted; exceptions are contained in ss
24 and 25.
