Science, Evidence and Logic
| Author | Mike Redmayne |
| Published date | 01 September 1996 |
| Date | 01 September 1996 |
| DOI | http://doi.org/10.1111/j.1468-2230.1996.tb02692.x |
REVIEW ARTICLE
Science, Evidence and Logic
Mike
Redmayne”
Bernard Robertson and
G.A.
Vignaux,
Interpreting Evidence: Evaluating
Forensic Science in the Courtroom,
Chichester: John Wiley
&
Sons, 1995,
xxi
+
240 pp, hb E24.95.
Introduction
Modern debates about the role of mathematical models in adjudicative fact-finding
are commonly traced back to
People
v
Collins.’
The Collinses were accused of
robbery, the case against them being largely that they fitted eyewitness descrip-
tions of the robbers. The prosecutor identified several characteristics of the
defendants, such as that the man had a moustache and that they drove a yellow car,
which matched the eyewitness descriptions. The prosecutor assigned probabilities
to the occurrence of each of the characteristics and, relying on the testimony of a
mathematics instructor who had described the product rule, multiplied these
probabilities together. He claimed that the resulting figure of 1/12,000,000
represented the probability of any couple possessing all of the characteristics of the
defendants. The jury convicted.
While the newspapers triumphantly announced that ‘Law of Probability Foils 2
Robbers
in
Tough Case,’* the Collinses appealed and their convictions were
overturned by
the
Supreme Court of California. There were two main problems
with the prosecutor’s strategy. First, the figures he used seemed to have been
plucked out of thin air: they lacked any objective grounding, while some of the
characteristics chosen were not independent, making use
of
the product rule for
independent events untenable. Secondly, even if the prosecutor could have proved
the validity of the calculations underlying the 1112,000,000 figure, it
was
not
obvious what the figure meant: it does not necessarily follow that there was only a
1/12,000,000 probability that the Collinses were inn~ent.~
Bayes’ theorem
Collins
was
important not only because it demonstrated the dangers of uninformed
probabilistic analysis, but also because it led to the suggestion that the way to avoid
*Faculty of Law, University of Manchester.
I
am grateful
to
John Jackson for his comments on
an
earlier draft. Responsibility for the views expressed
is,
of
course, mine alone.
1
(1968) 68 Cal 2d 319.
2 Quoted in Kingston, ‘Probability and Legal Proceedings’ (1966)
57
J
Crim Law, Criminology and
Police Science 93,
at
p93.
3 See Fairley and Mosteller, ‘A Conversation About
Collins’
(1974)
U
Chicago
L
Rev 243.
747
0
The Modern Law Review Limited 19% (MLR
595,
September). Published by Blackwell Publishers,
108
Cowley Road, Oxford
OX4
IJF
and 238
Main
Street, Cambridge, MA
02142.
USA.
To continue reading
Request your trial