1 Int'l J. Evidence & Proof 187 (1996-1997)
Presenting Probabilities in Court: The DNA Experience

handle is hein.journals/intjevp1 and id is 273 raw text is: Presenting probabilities in
court: the DNA experience
By Mike Redmayne
Lecturer in Law, University of Manchester
D he use of probabilistic' evidence in litigation has often been thought
to cause especial problems for the legal system. Much ink has been
spilt on arguments as to whether findings of liability can be based on
so-called naked statistical evidence.2 Another contentious issue has been
whether the use of probabilistic evidence somehow dehumanises the legal
system. The claim that it does has partly been the basis for a series of
decisions in which Minnesota's Supreme Court held that scientific evidence
should not be presented in probabilistic terms.3 Now the use of probabilistic
evidence, such as DNA evidence, is confronting the courts with a new
problem: that of explaining to juries just what the probability figure
associated with the evidence means. At first sight this problem might seem
trivial, but it is not. Britain's Court of Appeal has had to address the question
of the interpretation of DNA probabilities in a series of recent cases, but as yet
it has found no unproblematic solution.4 A Committee of the United States
National Research Council has also given the problem some thought, but it
has offered no clear recommendation on the issue.'
1 A distinction is sometimes made in the literature between 'probabilistic evidence' and 'overtly
probabilistic evidence', the point being that all evidence is probabilistic in that it can never
establish a proposition with certainty. I take this to be self-evident, and use 'probabilistic
evidence' to refer to testimony couched in numerical terms, whether it takes the form of
probability, odds or a likelihood ratio.
2 See generally Koehler, 'Probabilities in the Courtroom: An Evaluation of the Objections and
Policies' in Kagehiro and Laufer (eds), Handbook of Psychology and Law (Springer Verlag: New York,
1992).
3 For example, State v Carlson 267 NW 2d 170 (1978); State vBoyd 331 NW 2d 480 (1983). In a decision
which smacks of ad hocery, the Court has recently created a 'DNA exception' to its 'no
probabilities' rule: State v Bloom 516 NW 2d 159 (1994).
4 R.v Deen The Times, 10 January 1994; R v Dalby (unreported, CA no. 94/2819/W2 (1995)); R vAdams
[19961 2 Cr App R 467; R v Doheny, R v Adams The Times, 14 August 1996.
5 Though the Committee's call for more research on juror evaluation of probabilistic evidence is
welcome. See National Research Council, The Evaluation of Forensic DNA Evidence (National
Academy Press: Washington DC, 1996) 192-204.
THE INTERNATIONAL JOURNAL OF EVIDENCE & PROOF                                   187

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