Probability, Policy and the Problem of Reference Class
| Author | Robert J. Rhee |
| Published date | 01 October 2007 |
| Date | 01 October 2007 |
| DOI | http://doi.org/10.1350/ijep.2007.11.4.286 |
| Subject Matter | Article |
286 (2007) 11 E&P 286–291 E & P
PROBABILITY, POLICY AND THE PROBLEM OF REFERENCE CLASS
Probability, policy and
the problem of
reference class
By Robert J. Rhee*
Associate Professor of Law, University of Maryland School of Law
he mathematical concept of probability is relevant in evidentiary
assessment. The indeterminacy of fact-finding and legal assessment,
unique products of human intuition and intelligence, is well known. The
application of law is sometimes unpredictable, and thus the substitution of an
apparently formal methodology for a subjective process is alluring. But many
scholars, and more importantly courts, shun an overtly mathematised process.1In
most situations, probability as a mechanical output, while relevant, is neither
dispositive nor particularly weighty. Why is it so? And why should it be so? There
are many reasons.2This short article focuses on the problem of reference class as it
relates to probability and weight of evidence, and policies underlying legal rules.
Statistical probability requires a reference class from which a proportion is
derived.3In simple matters, of coin flips or sex of newborns, the appropriate
reference class is trivially obvious. However, as Ronald Allen and Michael Pardo
showed, evidentiary inquiries are seldom defined in such narrow symmetric
parameters.4Probability assessments change with the reference class. If a propo-
sition is subject to proportional comparison against two or more different
T
1 See e.g. People vCollins, 438 P 2d 33 (1968); Laurence H. Tribe, ‘Trial by Mathematics: Precision and
Ritual in the Legal Process’ (1971) 84 Harvard Law Review 1329.
2 See e.g. Ronald J. Allen and Michael S. Pardo, ‘The Problematic Value of Mathematical Models of
Evidence’ (2007) 36 Journal of Legal Studies 107; Charles Nesson, ‘The Evidence or the Event? On
Judicial Proof and the Acceptability of Verdicts’ (1985) 98 Harvard Law Review 1357; Tribe, above n. 1.
3 John Maynard Keynes, A Treatise on Probability (Macmillan: London, 1921) 94.
4 Allen and Pardo, above n. 2.
* Email: rrhee@law.umaryland.edu. I thank Brad Borden, Alex Glashausser and Bill Merkel for their
comments. I thank Ronald Allen for his generous invitation to participate in this symposium.
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