Law commission: Expert Evidence
UEA Climatic Research Unit.
Accusations of data manipulation.
House of Commons Science & Technology
Committee: ‘no intention to deceive’.
Independent Review by Lord Oxburgh:
“We cannot help remarking that it is very
surprising that research in an area that depends
so heavily on statistical methods has not been
carried out in close collaboration with
professional statisticians.”
Law Commission: Expert Evidence
• The problem of ‘messy data’
• Measurements from individual weather
stations simple; BUT
• Some countries have many stations, others
very few, and large areas of earth none.
• This can lead to over-simplification, and
dangerously misleading generalisation: eg
Intergov. Panel on Climate Change:
• Neglected discrepancy between direct and
‘proxy’ measurement such as tree ring data.
Law Commission: Expert Evidence
• Paper commissioned from Prof David Hand:
• Common sources of unreliability
• Statistics commonly match data to theories:
possible sources of error must be clear.
• E.g. false positive rate; percent & proportion.
• Theories must not predict too wide a range of
possible outcomes.
• Any ‘missing’ or ‘imperfect’ data must be
accounted for.
• Likewise possible sources of bias.
Law Commission: Expert
• Distinguish: Subjective honesty, subjectiveobjective fairness, objective reliability.
• Reliable enough for…..?
• Distinguish: Scholarly speculation; civil
litigation; criminal litigation.
• Possible failure of honesty or fairness: Sally
Clark (No.2) 2003. Prosecution expert fails
to disclose test result for one of two infants.
• Another expert in Clark faced ‘messy data’
problem: Cot death can be affected by
environmental/genetic factors.
Law Commission: Expert Evidence
• Clark: 2nd expert faced ‘fairness’ problems:
data giving 1 in 73 mil chance of two SIDS
cases in a family based on data that had
warning of other possible influential factors.
• Cannings (2004). Reliability fit for
purpose? ‘Dogma’ that 2 or more
unexplained infant deaths non-accidental.
• Harris (2005) Reliability fit for purpose?
Non-accidental head injury inferred from
particular triad of intra-cranial injuries.
Law Commission: Expert Evidence
• Lessons so far:
• 1. Accept that a great deal of expertise make
assumptions about matters outside its field.
• 2. Do not conceal ‘inconvenient’ data!
• 3. Be alert to purposes for which data
may/not prove reliable. What is fine for
scholarly speculation is a long way from
what can pass muster as only or key
evidence in the prosecution’s case.
• 4. Cannings/Harris: support evidence only?
Law Commission: expert evidence
Our aim is to reform the basis on which expert
evidence is admissible.
Expert evidence should only be admissible if the
trial judge is persuaded that it is sufficiently
reliable
The judge should be assisted by guidelines and
(if need be) a court expert
Law Commission: expert evidence
• What is the present law? Bonython (1984):
• Is the subject-matter of the opinion part of, “a
body of knowledge or experience which is
sufficiently organised or recognised to be
accepted as a reliable body of knowledge or
experience”, such that a special knowledge of it
will make the witnesses opinion helpful?
• In Luttrell [2004], the CA rejected the view
that, to be admissible, there is a preliminary
requirement that expert evidence involve a
methodology that can be tested in cross-e.
Law Commission: expert evidence
• There are problems of over and underinclusiveness with the Bonython test.
• Over inclusiveness: Cannings (2004), cot death;
Harris (2005), shaken baby syndrome.
• Under-inclusiveness: Some expert evidence that
does not meet the Bonython criteria may
nonetheless be perfectly reliable:
• See Gilfoyle (no.2) (2001)). See, by contrast
Robb (1991); Harris (2005).
Law Commission: expert evidence
• Voice identification based solely on
auditory comparison
• Handwriting comparisons
• Diagnoses of battered womens’ syndrome
• Repression theory of sex abuse memory
• ‘Gait’ comparison
• Unreliable evidence: Dallagher (2002)
• Problem of experience-based expertise
Law Commission: Expert Evidence
• CPS guidelines for LCN DNA evidence:
• Establish forensic scientist’s qualifications.
• Check procedures in lab to avoid
contamination. Does lab have documented
processes?
• Does evidence involve composite results?
• How were profile results interpreted?
• Were there variations or lack of reducibility
in results?
Law Commission: Expert Evidence
• HC Science and Technology Committee:
• “An objective, clearly defined test to
establish whether a theory or technique is
sufficiently robust…to merit
admission…[is] highly attractive” (2004-5).
• Rule 702 of the Federal rules of Evidence,
“If scientific…or other specialised
knowledge will assist the trier of fact…a
witness qualified by knowledge, skill,
experience, training or education, may
testify thereto..”
Law Commission: Expert Evidence
• Daubert v Merrell Dow (1993):
• 1. Ordinarily a key question is whether the
theory or technique can be/has been tested.
• 2. Has the theory or technique been
subjected to peer review/publication?
• 3. With particular techniques, the Ct should
consider the known or potential error rate,
and any standards for monitoring this.
• 4. Widespread acceptance is important;
techniques with minimal support should be
viewed sceptically.
Law Commission: expert evidence
• Our provisionally proposed solution, following
Daubert.
• 1. A ‘gate-keeping’ role for the trial judge.
• 2. This involves a discretion to exclude
otherwise relevant evidence, on grounds of
unreliability.
• 3. Discretion to be informed by guidelines on
reliability.
• 4. In difficult cases, judge to have power to call
on an independent assessor.
Law Commission: expert evidence
• General: expert opinion admissible only if
the court deems it sufficiently reliable.*
• Question of law: evidence predicated on
sound principles, techniques, assumptions.
• Question of fact: these principles etc have
been properly applied in the case.
• Question of fact: the evidence is supported
by those principles etc as applied to the
facts of the case.
• Party relying on evidence must prove.*
Law Commission: expert evidence
• Responses: over 80 individuals and
organisations responded, mainly to support.
• A selection of observations for
improvement or change:
• “Need for a warning to the jury that expert
evidence can be wrong” (a solicitor).
• In child death/injury cases, expert should
come from separate health authority
(campaigner).
Law Commission: expert evidence
• Responses (cont.):
• “Need to add to criteria: (a) attention to
possible variations in the meaning of the
opinion or its wording, (b) attention to
whether expert’s confidence is accurately
expressed, (c) does opinion addresses other
explanations” (academic specialist).
• Proposals should be extended to civil
proceedings (several consultees).
Law Commission: expert evidence
• Responses (cont.):
• Experts must be properly prepared, and
produce a written submission supporting
methodology (specialist organisation).
• There should be specialist working parties
looking at science disciplines (like the one
for forensic science) who could issue codes
of practice (scholar).
• Needs to be an inquisitorial stage where
judge, experts and parties appraise evidence
(senior judge).
Law Commission: expert evidence
• Responses (cont.):
• ‘Orthodoxy’ should be shown to be reliable
and trustworthy before being admitted
(campaigner).
• Proposals should apply to expert
assessments that an offender is ‘dangerous’,
at the sentencing stage (lawyers’
organisation).
Law Commission: expert evidence
• What are we now considering (A)?
• 1. Court focus in testing admissibility
should not just be on reliability, but also
competence, impartiality, strength of
opinion, necessity of the evidence for jury.
• 2. Judge to follow a single set of generic
guidelines, not divided between scientific
and non-scientific expertise.
• 3. Judge to rule of the scope of an expert’s
area of expertise at the start.
Law Commission: expert evidence
• What are we now considering (B)?
• Trial judge to be allowed (i) to call informal
hearing with parties/experts to discover
precise extent of disagreement, and (ii) to
make an order enabling the creation of a
single document for the jury on outcome.
• Defence will not have to go through hoops
simply to rebut prosecution case, but they
will if their case hinges on a ‘new theory’.
• Judicial duty to consider a warning in some
cases that expert opinion can be wrong.
Law Commission: expert evidence
• Specific consideration for experts:
• 1. They must be prepared to defend their
methodology, not just their evidence. A role
for professional bodies in producing
guidelines?
• 2. Such methodological material should be
disclosed to the other side.
• 3. Over-riding duty is to the court. So, if
called to give evidence of probability of an
event, assuming P’s case is true, they should
be ready to do the same, if D’s case is true.