The Law Commission has published "Expert Evidence in Criminal Proceedings in England and Wales" (Law Com No. 325 - 21st March 2011). The Commission's Report contains many recommendations relating to the admissibility of expert evidence in criminal proceedings in England and Wales. There is also a Draft Bill - set out at Appendix A of the report (page 144). The Commission has stated: "Too much expert opinion evidence is admitted without adequate scrutiny because no clear test is being applied to determine whether the evidence is sufficiently reliable to be admitted" - see Law Commission for their fuller statement.
- the court must be satisfied that it would provide information which is likely to be outside a judge or jury’s experience and knowledge, and which would give them help they need in arriving at their conclusions
- the witness must be qualified to give the evidence;
- the evidence is not made inadmissible as a result of clause 3 (impartiality)
- In addition, expert opinion evidence is admissible in criminal proceedings only if it is sufficiently reliable to be admitted (see clause 4).
might think that the first three bullet points are obvious. They are included because the Commission wished to put in a single piece of legislation all the relevant law relating to admissibility of this type of evidence. They key new feature is the proposed reliability test which is set out in Clause 4 and Schedule 1 of the Draft Bill.
A reliability test
The decision on reliability would be for the trial judge alone. Under Clause 4, expert opinion evidence is sufficiently reliable if (a) the opinion is soundly based, and (b) the strength of the opinion is warranted having regard to the grounds on which it is based. Certain matters could, in particular, provide a reason for determining that expert opinion evidence is not sufficiently reliable: (a) the opinion is based on a hypothesis which has not been subjected to sufficient scrutiny (including, where appropriate, experimental or other testing), or which has failed to stand up to scrutiny; (b) the opinion is based on an unjustifiable assumption; (c) the opinion is based on flawed data; (d) the opinion relies on an examination, technique, method or process which was not properly carried out or applied, or was not appropriate for use in the particular case; (e) the opinion relies on an inference or conclusion which has not been properly reached.
When assessing the reliability of expert opinion evidence, the court must have regard to (a) such of the generic factors set out in Part 1 of the Schedule as appear to the court to be relevant; (b) if any factors have been specified in an order made under Part 2 of the Schedule in relation to a particular field, such of those factors as appear to the court to be relevant; (c) anything else which appears to the court to be relevant.
(a) The extent and quality of the data on which the opinion is based, and the validity of the methods by which they were obtained.
(b) If the opinion relies on an inference from any findings, whether the opinion properly explains how safe or unsafe the inference is (whether by reference to statistical significance or in other appropriate terms).
(c) If the opinion relies on the results of the use of any method (for instance, a test, measurement or survey), whether the opinion takes proper account of matters, such as the degree of precision or margin of uncertainty, affecting the accuracy or reliability of those results.
(d) The extent to which any material upon which the opinion is based has been reviewed by others with relevant expertise (for instance, in peer-reviewed publications), and the views of those others on that
(e) The extent to which the opinion is based on material falling outside the expert’s own field of expertise.
(f) The completeness of the information which was available to the expert, and whether the expert took account of all relevant information in arriving at the opinion (including information as to the context of any facts to which the opinion relates).
(g) Whether there is a range of expert opinion on the matter in question; and, if there is, where in the range the opinion lies and whether the expert’s preference for the opinion proffered has been properly explained.
(h) Whether the expert’s methods followed established practice in the field; and, if they did not, whether the reason for the divergence has been properly explained.
The Commission states that the test would not need to be applied routinely or unnecessarily but it would be applied in appropriate cases and it would result in the exclusion of unreliable expert opinion evidence. Under the test, expert opinion evidence would not be admitted unless it was adjudged to be sufficiently reliable to go before a jury. (It is a moot point whether a jury would then be more inclined to accept such evidence since they would probably know that it had passed the judge before they heard it ?).
If a trial is in the Magistrates' Courts, the Commission say that the admissibility must be decided by a District Judge (Magistrates' Courts) who should (according to the Commission) provide a written admissibility ruling, and then the judge should ordinarily try the case. There may be some exceptions to this which will be specified in Criminal Procedure Rules. The Commission add that they - accept that magistrates' courts should have the power to allocate the trial to a bench of lay magistrates, if it is unnecessary for a District Judge to continue with the case."
Other jurisdictions and other material:
"Reliability" tests are not unknown in other jurisdictions. For instance, the Supreme Court of the USA has developed a test (sometimes referred to as "Daubert" from the case of Daubert v Merrell Dow Pharmaceuticals 509 US 579 (1993) though the origins of the rest are older. See also Federal Rules of Evidence (Rule 702). The Daubert test has been criticised as insufficiently effective in criminal cases - see the Law Commission's report for further discussion.
The House of Commons Science and Technology Committee 7th Report of Session 2004-5 "Forensic Science on Trial" and the Labour Government's response to that report.
A leading book in this area is "Expert Evidence: Law and Practice" by Tristram Hodgkinson and Mark James.
See also: the Solicitor's Journal view of the report ..... Government review of Forensic Science Research and Development (Home Office) ..... and Law and Lawyers Forensic Science Service to be wound up