The Epistemology of Statistical Evidence

AuthorAmit Pundik
Published date01 April 2011
Date01 April 2011
DOIhttp://doi.org/10.1350/ijep.2011.15.2.373
Subject MatterArticle
THE EPISTEMOLOGY OF STATISTICAL EVIDENCE
The epistemology of
statistical evidence
By Amit Pundik*
Tel Aviv University
Abstract Numerous accounts have been suggested to explain differences
between statistical and individualised evidence and to justify restrictions on the
use of statistical evidence in court. A dominant direction in such accounts is the
idea that statistical evidence is lacking in some certain quality, making it
epistemologically unwarranted for establishing the fact it is introduced to prove.
Among the qualities suggested are luck, appropriate causal connection, weight,
and case-specificity. Epistemic accounts thus constitute attempts to identify an
intrinsic quality which individualised evidence (such as eyewitness testimony,
confession, the individual’s medical records) has but statistical evidence lacks, a
quality which makes inference from the statistical evidence to the particular
case epistemologically deficient. To the existing debate around epistemic
accounts, this article adds several generic and inherent problems from which
any epistemic account suffers. Based on these generic problems, it is concluded
that the epistemic direction lacks potential. If there is any justification for
restricting the use of statistical evidence in court, it does not lie in episte-
mology; it has to lie elsewhere.
Keywords Probability; Accuracy; Cohen; Bayes; Policy
e need both theoretically and practically to distinguish between those
types of statistical evidence which should be used in court and those
types which should not be used in court. In particular, case law seems to
lack a systematic approach to statistical evidence.1On the one hand, statistical
evidence is regularly adduced in litigation. For example, statistics are used in
doi:10.1350/ijep.2011.15.2.373
THE INTERNATIONAL JOURNAL OF EVIDENCE & PROOF (2011) 15 E&P 117–143 117
1 In the United States, statistical evidence was rejected in cases such as Cimino vRaymark Industries
151 F 3d 297 (5th Cir 1998); In re Fibreboard Corporation 893 F 2d 706 (5th Cir 1990), but was deployed
in Blue Cross vPhilip Morris 113 F Supp 2d 345 (EDNY 2000); Hilao vEstate of Marcos 103 F 3d 767 (9th Cir
1996). For descriptive research on the use of statistical evidence in US courts, together with an
attempt to identify patterns when statistical evidence is used or rejected, see J. J. Koehler, ‘When
Do Courts Think Base Rate Statistics Are Relevant?’ (2002) 42 Jurimetrics Journal 373.
W
* Email: amitp@post.tau.ac.il. I am grateful to Adrian Zuckerman, John Gardner, David Enoch and
the anonymous referee for their helpful comments. I am also indebted to Elizabeth Pender and Uri
Preisman for their valuable technical assistance and to the PHG foundation for its generous
financial support.
relation to DNA evidence (to calculate the probability of a random DNA match in
criminal identification and civil parentage cases);2compensation for loss of
earnings (to calculate the life expectancy which the claimant would have enjoyed
had the defendant not unlawfully harmed her);3toxic torts (to prove causation);4
medical law (to prove loss of chance);5human rights (to prove the extent of
damage caused by the violation of the claimant’s human rights);6product liability
(to determine the market share for proportionate market-share liability);7
employment law (to prove group-based discrimination);8and competition law (to
calculate the economic damage resulting from price fixing).9On the other hand,
some types of statistical evidence have been subject to strong intuitive objections
in some well-known examples, both hypothetical and real. Statistical evidence has
been notoriously misused in some criminal cases. For instance, at the end of the
19th century in France, Alfred Dreyfus was convicted of treason after statistical
evidence was used creatively to prove his identity as the author of documents
118 THE INTERNATIONAL JOURNAL OF EVIDENCE & PROOF
THE EPISTEMOLOGY OF STATISTICAL EVIDENCE
2 For the criminal context, see RvDoheny and Adams [1997] 1 Cr App R 369. For the civil context, see
Family Law Reform Act 1969, s. 20 and N. Lowe and G. Douglas, Bromley’s Family Law, 10th edn
(Oxford University Press: Oxford, 2007) 325–31.
3 In comparison with the United States, the use of actuarial statistical methods is relatively limited
in the United Kingdom and preference is given to a simpler multiplicand and multiplier method.
See Hunt vSevers [1994] 2 AC 350, HL and S. Deakin, A. Johnston and B. Markesinis, Markesinis and
Deakin’s Tort Law, 6th edn (Oxford University Press: Oxford, 2007) 986. However, whether it is
acknowledged or not, even this method of calculation relies on some statistical evidence (e.g.
average longevity). For comparative work between the English methods and actuarial methods
which are used in the United States, see R. Lewis, R. McNabb, H. Robinson and V. Wass, ‘Court
Awards of Damages for Loss of Future Earnings: An Empirical Study and an Alternative Method of
Calculation’ (2002) 29 Journal of Law and Society 406. Based on their empirical findings, the authors
criticise the English system for under-compensating claimants.
4 Such evidence played a key role in the tobacco litigation (see, e.g., Blue Cross vPhilip Morris 113 F
Supp 2d 345 (EDNY 2000)). However, in other cases such evidence was rejected (see, e.g., the
asbestos cases Cimino vRaymark Industries 151 F 3d 297 (5th Cir 1998) and In re Fibreboard Corporation
893 F 2d 706 (5th Cir 1990)).
5Gregg vScott [2005] UKHL 2. The claim failed, but this case is still an example where statistical
evidence was admitted and used, even though the facts established by the evidence were
insufficient to support the claim.
6Hilao vEstate of Marcos 103 F 3d 767 (9th Cir 1996).
7Sindell vAbbott Laboratories 26 Cal 3d 588 (1980); In re ‘Agent Orange’ Product Liability Litigation 597 F
Supp 740 (EDNY 1984).
8 Perhaps the most notable case in this area is a class action of gender discrimination on behalf of
two million women against Walmart, the world’s largest private employer (see Dukes vWal-Mart Inc
(Dukes I) 222 FRD 137 (ND Cal 2003)). The decision to grant the claimants a class action certificate
was affirmed by the 9th Circuit Court first in 2007 (see Dukes vWal-Mart Inc (Dukes III) 474 F 3d 1214
(9th Cir 2007)) and then again in 2009(Dukes vWal-Mart Stores Inc.(Duke IV) No. 04-16688 (9th Cir Apr
26, 2010); the judgment can be found at <http://www.ca9.uscourts.gov/datastore/opinions/2010/
04/26/04-16688.pdf>, accessed 14 January 2011). The admission of such evidence in support of
discrimination is not new (see Alabama vUnited States 304 F 2d 583 (5th Cir) aff’d, 371 US 37 (1962)
and, more recently, Caridad vMetro-North Commuter Railroad 191 F 3d 283 (2d Cir 1999)).
9United States vColumbia Pictures 25 FRD 497 (SD New York 1960).

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