Away from the Numbers: Opinion in the Court of Appeal
| Author | Adam Wilson |
| Date | 01 December 2011 |
| Published date | 01 December 2011 |
| DOI | 10.1350/jcla.2011.75.6.739 |
| Subject Matter | Article |
Away from the Numbers:
Opinion in the Court of Appeal
Adam Wilson*
Abstract The Court of Appeal has recently addressed opinion evidence in
numerous cases. Recurring themes have been addressed consistently with
the exception of R v T(2010). It is suggested that the rationale in Tis not
as persuasive as that adopted in other cases. This article advocates that,
where appropriate, a Bayesian approach should be adopted. In favouring
a Bayesian approach it is suggested that ambiguous phrases such as
‘scientific method’ may not serve courts effectively and judges have been
correct, in the majority of cases, to approach opinion evidence in a
pragmatic, case-specific fashion. The Court of Appeal warrants credit for
emphasising the importance of pre-trial hearings and robust case
management.
Keywords Bayes; Opinion evidence; Expert testimony; Forensic
testimony; Forensic science
The Court of Appeal has recently addressed opinion evidence in numer-
ous cases. Case management to identify issues in dispute, and ensure
clear presentation, has helpfully been emphasised. The court has also
broached the parameters of admissibility and recurring themes have
been addressed consistently with the exception of Rv T.1The rationale in
Tis not as persuasive as that adopted in other cases. This article suggests
that attempts to define largely meaningless phrases, such as ‘scientific
method’, may not serve as effectively as an understanding of the
Bayesian approach.
A trite observation is the law governs opinion evidence not forensic
science per se. Given this wide spectrum only ‘sufficient reliability’2is
required. The Law Commission’s Consultation Paper helpfully identified
two checklists for admission, one for scientific disciplines and one for
experience-based disciplines.3In response to feedback the Law Commis-
sion’s Recommendation Report adopted one set of guidelines as there
was no clear line separating science from non-science.4The gamut of
disciplines negates common semantics and vague phrases may elicit a
multiplicity of meanings and perceptions.
* Senior Lecturer in Law, Sheffield Hallam University; e-mail:
A.J.Wilson@shu.ac.uk.
1 [2010] EWCA Crim 2439, [2011] 1 Cr App R 9.
2RvReed and Reed [2009] EWCA Crim 2698, [2010] 1 Cr App R 23 at [111]; Rv
Weller [2010] EWCA Crim 1085 at [34] [37]; RvBroughton [2010] EWCA Crim
549 at [36]–[37]; Rv T [2010] EWCA Crim 2439, [2011] 1 Cr App R 9 at [86].
3 Law Commission, The Admissibility of Expert Evidence in Criminal Proceedings in
England and Wales, Law Com. Consultation Paper No. 190 (2009) paras 6.26–6.35,
available at http://www.justice.gov.uk/lawcommission/expert-evidence-in-criminal-trials.
htm, accessed 28 September 2011.
4 Law Commission, Expert Evidence in Criminal Proceedings in England and Wales, Law
Com. Report No. 325 (2011) para. 3.45, available at http://www.justice.gov.uk/law
commission/expert-evidence-in-criminal-trials.htm, accessed 28 September 2011.
503The Journal of Criminal Law (2011) 75 JCL 503–527
doi:10.1350/jcla.2011.75.6.739
Requests for ‘logical’ argument may lack definition.5The term ‘sci-
entific methodology’ is also problematic. Professor Haack states:
Scientific inquiry is continuous with the most ordinary of everyday empir-
ical inquiry. There is no mode of inference, no ‘scientific method’, exclusive
to the sciences . . . as far as it is a method, it is what . . . the rest of us do
when we really want to find something out: make an informed conjecture
. . . check how it stands up to the best evidence we can get, and then use
our judgment whether to accept it.6
In criminal trials events only occur once, and evidence must be pro-
tected, recorded, collected, analysed, interpreted, evaluated and pre-
sented.7Evidence may be lost before it can be protected. Investigators
form a subjective hypothesis determining how to process the crime
scene. Investigators may not know how partial their evidence is or what
evidence they lack. Trials require subjective judgment. Subjective prob-
ability is called ‘Bayes’.
Investigations, whilst subjective, must be rational. Research assists
rationality, but is not a panacea. Research proceeds from individual
examples to generic principles via inductive logic. Inductive logic sug-
gests, but does not ensure, truth. Research may suffer from small
databases8and whether generalisation is appropriate remains moot. It is
debatable whether Locard’s principle, that every contact leaves a trace, is
a scientific principle or an abstraction.9
Variables make extrapolating generic principles problematic. Assess-
ing whether DNA transfers from one person to another requires assess-
ment of the orifice touched, fingernail length, when, how well and with
what hands were washed, differences in skin, whether people bite their
nails, whether they contacted with their dominant or non-dominant
hand. Any methodology may be criticised. Researchers may ask people
to wash their hands, prior to testing, to prevent contamination. This
leaves open the criticism that loose cells may have been displaced
obscuring results.10 Research may suggest one conclusion which, over
time, fails to be replicated.11 Requiring research may also uphold the
5 Inductive, deductive, mathematical or philosophical? Logical arguments may be
wrong.
6 S. Haack, Defending Science Within Reason (Prometheus Books: 2007) 24.
7 A. Jamieson, ‘The Philosophy of Forensic Scientific Identification’ (2008) 59
Hastings LJ 1031.
8 E. Dowlman, N. Martin, M. Foy, T. Lochner and T. Neocleous, ‘The Prevalence of
Mixed DNA Profiles on Fingernail Swabs’ (2010) 50(2) Science & Justice 64 (sample
of 40); N. Flanagan and C. McAlister, ‘The Transfer and Persistence of DNA under
the Fingernails Following Digital Penetration of the Vagina’ (2010) Forensic Sci Int
Genet, doi: 10.1016/j.fsigen.2010.10.008 (sample 8 couples on transfer and 4 on
persistence). This is not intended as criticism.
9 I. Evett, ‘A Quantitative Theory for Interpreting Transfer Evidence in Criminal
Cases’ (1984) 33(1) Appl Statist 25.
10 Flanagan and McAlister, note 8 above at [4].
11 A. Lowe, C. Murray, J. Whitaker, G. Tully and P. Gill, ‘The Propensity of
Individuals to Deposit DNA and Secondary Transfer of Low Level DNA from
Individuals to Inert Surfaces’ (2002) 129 Forensic Sci Int 25–34 was not replicated
in M. Phipps and S. Petricevic, ‘The Tendency of Individuals to Transfer DNA to
Handled Items’ (2007) 168 Forensic Sci Int 162 at [4].
The Journal of Criminal Law
504
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