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J S Publications’ summary of the Law Commission’s Proposals
The following is our summary of the Consultation Paper. After reading this, you can:
The problem with expert evidence in criminal trials
The steady stream of criminal appeals over recent years featuring the criticism of expert evidence has led many commentators to call for the accreditation of individual expert witnesses. However, much of the criticism of expert evidence has been unfounded. It often was not the expert opinion itself that was the root cause of a miscarriage, but the court's willingness to choose between the conflicting opinions of (often) eminent experts. When this happens in a case featuring little evidence other than the expert evidence, then there is a much-increased risk of a miscarriage of justice being perpetrated.
Dangers in the current system – the need for change
The criminal courts in England and Wales currently adopt a liberal approach to the admission of expert evidence. In effect, providing the court is convinced that the proposed expert evidence is relevant to some issue in the case, it will allow the evidence to be adduced. It is then for the parties to test the expert evidence through the adversarial process, and finally for the court to determine what evidential weight ought to be applied.
Expert evidence is unique in that it can be, and often is, opinion evidence. We believe that the unique nature of expert evidence requires special treatment if it is to inform, rather than mislead, the court. The practical effect of the liberal approach is that it is fairly easy for a party to get speculative opinion evidence admitted into a trial, it just has to be relevant and potentially useful. But in the current procedural framework, it is not until the trial itself arrives that the competing expert evidence is tested.
When testing factual evidence at trial, it is unlikely that the court will be drawn into philosophical considerations – all that is to be tested is whether the witness is honest and truthful. When testing conflicting opinion evidence, it is very likely that the court will be dragged into consideration of the methodological underpinnings of the science and whether the opinion being offered is logically consistent with the results of the analytical methods adopted. Such matters can become complex, and those involved deserve the opportunity for quiet reflection. The trial is not, we think, that well suited to this task.
It seems clear that there is scope to improve the way in which the criminal courts handle expert evidence.
Admissibility of expert evidence
The Law Commission highlights four factors that control the admissibility of expert evidence in common law in England and Wales. These are (to paraphrase the Bonython case1 for the first three), that:
- the subject matter requires expertise to understand
- the subject matter is drawn from a body of work that is sufficiently well developed as to be ‘reliable’
- the person giving the evidence is an expert in the subject matter, and
- the expert must be capable of giving an impartial opinion.
The Law Commission’s proposals for change relate only to the second of these factors, the underlying reliability of the proffered expert evidence.
The Law Commission starts by explaining why it believes the present approach to determining the evidentiary reliability of expert evidence (by reference to whether or not it comes from a reliable body of knowledge) is proving problematic. It then looks at four possible options for change:
Option 1: reformulate in statute the current common law discretion a judge has to exclude expert evidence that is found to be ‘irrelevant’ but give no guidance on how to determine irrelevance.
Option 2: reformulate in statute the current common law discretion a judge has to exclude expert evidence that is found to be ‘irrelevant’ but provide structured guidance on how to decide evidentiary reliability.
Option 3: defer to the consensus of experts on whether any given evidence should be admissible.
Option 4: introduce a test that requires the trial judge to address the reliability of the evidence in question, instead of simply deferring to the general view of experts in the field. The court is therefore fully accountable for its decision to admit or exclude any expert evidence tendered before it.
Ultimately the Law Commission chooses Option 4, and proposes a new statutory test for determining the admissibility of expert evidence in criminal proceedings. This test would provide that expert evidence is admissible only if the court is satisfied that the evidence is sufficiently reliable to be admitted. In determining if the test is satisfied, the court would have to refer to a statutory list of guidelines. In effect, the Law Commission proposes creating a new 'gate-keeper' function for the court. The Law Commission believes that this process should apply equally to the prosecution and the defence.
Types of gate-keeping
There are two main gate-keeper tests that are commonly discussed: the Frye test and the Daubert test. Both are based upon decisions of the US Supreme Court.
The Frye test admits evidence based upon theory that is sufficiently established to have gained general acceptance in the particular field in which it belongs. This kind of test excludes novel science. It is, in effect, the deference test in Option 3 above.
The Daubert test entails a preliminary assessment of whether the reasoning or methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology can be applied properly to the facts in issue. The Law Commission test is a form of the Daubert test.
Whilst making plain that many factors will bear on a Daubert assessment, the US Supreme Court has given four observations on possible factors.
- Can the theory or technique in question be tested?
- Has the theory or technique been subjected to peer review and publication?
- In the case of a particular scientific technique, what are the known or potential rates of error and do standards of maintenance exist to control the technique’s operation?
- Widespread acceptance can be an important factor in ruling particular evidence admissible. A known technique which has been able to attract only minimal support within the relevant scientific community may properly be viewed with scepticism.
The Daubert approach is not without its distractors. There are concerns about what is meant by ‘scientific method’ because clearly not all expert evidence is scientific. There is also criticism of the use of peer review as any measure of evidentiary reliability. And there are those who do not believe that the judiciary (who are generally not scientists) have the ability to apply the test in practice.
The Law Commission Proposals
Proposal 1: A gate-keeper role
The Law Commission’s key proposal is that there should be an explicit 'gate-keeping' role for the trial judge with a clearly defined test for determining whether proffered expert evidence is sufficiently reliable to be admitted. The application of this test would determine whether the tendered evidence is admissible as a matter of law.
After first determining that the proposed expert evidence is logically relevant to the disputed matter, that it would provide the jury with substantial assistance and that the witness is truly expert and able to provide an impartial opinion, the judge would need to address the gate-keeping question. The question is: Is the evidence is sufficiently reliable to be considered, and ultimately accepted, by a Crown Court jury?
So the Law Commission proposes that there should be a statutory provision along the following lines:
(1) The opinion evidence of an expert witness is admissible only if the court is satisfied that it is sufficiently reliable to be admitted.
(2) The opinion evidence of an expert witness is sufficiently reliable to be admitted if:–
(a) the evidence is predicated on sound principles, techniques and assumptions;
(b) those principles, techniques and assumptions have been properly applied to the facts of the case; and
(c) the evidence is supported by those principles, techniques and assumptions as applied to the facts of the case.
(3) It is for the party wishing to rely on the opinion evidence of an expert witness to show that it is sufficiently reliable to be admitted.
Thus, the trial judge would not only consider the reliability of the expert’s hypothesis, methodology and assumptions, but he would examine how the expert has applied them to the case and, if properly applied, whether the expert’s conclusion is logically sustainable.
Such a test would put experts on notice that they will be expected to provide the trial judge with evidence about the basis of their expert opinion sufficient to enable the judge to conclude that their evidence would provide the jury with reliable information.
Acknowledge the distinction between scientific and experiential expertise
While much expert evidence is based in science, there is also the type of expert evidence based on experience (e.g. forensic accountancy or experts in custom and practice for a particular trade). The Law Commission recognises this. It proposes two distinct sets of guidelines to cover each type of expert evidence.
For scientific expert evidence it proposes the following:
In determining whether scientific (or purportedly scientific) expert evidence is sufficiently reliable to be admitted, the court shall consider the following factors and any other factors considered to be relevant:
(a) whether the principles, techniques and assumptions relied on have been properly tested, and, if so, the extent to which the results of those tests demonstrate that they are sound;
(b) the margin of error associated with the application of, and conclusions drawn from, the principles, techniques and assumptions;
(c) whether there is a body of specialised literature relating to the field;
(d) the extent to which the principles, techniques and assumptions have been considered by other scientists – for example in peer-reviewed publications – and, if so, the extent to which they are regarded as sound in the scientific community;
(e) the expert witness’s relevant qualifications, experience and publications and his or her standing in the scientific community;
(f) the scientific validity of opposing views (if any) and the relevant qualifications and experience and professional standing in the scientific community of the scientists who hold those views; and
(g) whether there is evidence to suggest that the expert witness has failed to act in accordance with his or her overriding duty of impartiality
It would be for the trial judge to determine whether a field of expertise is to be classified as scientific and assessed in accordance with these guidelines. With regard to factor (a), the expert would need to show that the experimental or observational tests were conducted in an objective, scientifically valid way with appropriate comparators (for example, control groups) and safeguards (for example, measures to protect against contamination).
For experiential expert evidence it proposes the following guidance:
In determining whether experience-based expert evidence is sufficiently reliable to be admitted, the court shall consider the following factors (where applicable) and any other factors considered to be relevant:
(a) the expert’s qualifications, practical experience, training and publications and his or her standing in the professional or other expert community;
(b) the extent to which the basis and validity of the expert’s opinion can be explained, with particular reference to:
i. the extent to which the basis of the opinion (for example, any assumption relied upon) has been verified or discredited;
ii. the specific instances which support the claim to experience-based expertise;
iii. the bearing those instances have on the matter(s) in issue; and
iv. whether the expert’s methodology or reasoning has previously resulted in a demonstrably valid or erroneous opinion;
(c) whether there is a body of specialised literature relating to the field of expertise and, if so:
i. the extent to which it supports or undermines the expert’s methodology and reasoning; and
ii. the extent to which the expert’s methodology and reasoning are recognised as acceptable amongst his or her peers;
(d) whether there is evidence to suggest that the expert has failed to act in accordance with his or her overriding duty of impartiality.
Based on this guidance, the reliability of expert testimony on forensic document examination would be determined on the basis of, amongst other things, the witness’s experience, the number of standard points of comparison used and a detailed description of the process by which the expert reached the given opinion.
In the areas of professional, non-scientific expertise where there are well-accepted practices and methodologies, e.g. accountancy, it should be sufficient that the expert followed accepted practices and has provided a sufficient explanation of what was done.
Proposal 2: The onus of persuasion
The Law Commission proposes that any party to an action, or the judge, should be able to raise the question of evidential reliability as a preliminary issue. If raised,
- the judge could take 'judicial notice' of the evidentiary reliability of the proposed evidence if reliability has already been clearly established (and no new developments have arisen), or
- if the expert evidence is patently unreliable (e.g. a party wishes to adduce expert evidence from an astrologer), the judge could hold that it is inadmissible without the need for detailed investigation, or
- the judge would investigate the evidentiary reliability of the proffered expert evidence in accordance with the three-stage test. The party tendering the evidence would need to demonstrate that the expert’s hypothesis and methodology comprise a reliable basis for the expert testimony. In accordance with the Criminal Procedure Rules, the expert would have a duty to provide details of research findings that undermine the validity of his hypothesis or reasoning.
Importantly, at no stage of this inquiry into the reliability of the underpinning body of knowledge is it incumbent on the judge, the parties or the experts to show or determine if the opinion given by the expert is actually correct. The test is only whether the opinion is grounded in a body of knowledge that is itself deemed reliable.
Further issues
Court-appointed assessor
It would be for the trial judge to provide a reasoned decision on admissibility with reference to the criteria for assessing evidentiary reliability. Nevertheless, in determining whether expert scientific evidence is sufficiently reliable to be admitted, the Law Commission sees merit in an argument that the judge should exceptionally (that is, in cases where the evidence or field is particularly difficult) be permitted to call upon an independent assessor to provide assistance and guidance.
Education
The Law Commission believes that judges (and criminal practitioners) should receive practical training on the methodology of science, the standards for determining the statistical significance of research findings and how to determine the reliability of experience-based expertise.
Accreditation
The Law Commission believes that if a system of non-compulsory accreditation of expert witnesses is encouraged, and the process of accreditation were to provide a further hallmark of reliability, there is no reason why the judge should not take into account, as an additional relevant consideration, the fact that an expert witness is or is not accredited when addressing the evidentiary reliability of his expert evidence.
Footnotes
1 (1984) 38 SASR 45, 46 to 47 (Supreme Court of South Australia)
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