Expressing evaluative forensic science opinions in a court of law

Law, Probability and Risk

Volumn 11, Issue 4, 2012, Pages 289-302

  Ligertwood, Andrew ^a   Edmond, Gary ^b  

^a UNIVERSITY OF ADELAIDE   (Australia)

^b UNIVERSITY OF NEW SOUTH WALES   (Australia)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 84871338017     PISSN: 14708396     EISSN: 1470840X     Source Type: Journal    
DOI: 10.1093/lpr/mgs016     Document Type: Article

References (50)

1. [2010] EWCA Crim 2439.
2. Our attention is directed to what transpires, or should transpire, in court rather than to what forensic scientists should do in their investigations and how they should express conclusions in reports or in other contexts. See B. Found and G. Edmond, 'Reporting on the comparison and interpretation of pattern evidence: Recommendations for forensic specialists' (2012) 44 Australian J Forensic Sci 193-6.
3. M. Redmayne, P. Roberts, C. Aitken, and G. Jackson, 'Forensic science evidence in question' (2011) Crim LR 347.
4. Forensic science evidence cannot assist the jury if it is not reliable. Similarly, evidence that is likely to be overvaluedwill not assist the jury's decision-making responsibilities.
5. See references at n 18 below.
6. See Guest editorial, Expressing evaluative opinions: A position statement (2011) 51 Sci & Justice 1-2 (while a number of lawyers also joined as signatories to the editorial its instigation appears to lie with the forensic science community). See also G. Morrison, 'The likelihood-ratio framework and forensic evidence in court: A response to R v T' 16 Int J Evidence and Proof 1-29.2012
7. R v T EWCA Crim 2439 at [30].2010
8. R v T [2010] EWCA Crim 2439 at [73], [96]. On juror understanding of forensic science terminologies see D. McQuiston-Surrett, and M.J. Saks, 'The testimony of forensic identification science: What expert witnesses say and what factfinders hear' (2009) 33 Law & Human Behavior 436 and D. McQuiston-Surrett and M. Saks, 'Communicating opinion evidence in the forensic identification sciences: accuracy and impact' (2008) 59 Hastings Law J 1159
9. We emphasise that this essay is not intended as a defence of the present system.
10. Guest Editorial, 'Expressing evaluative opinions': '1) The interpretation of scientific evidence invokes reasoning in the face of uncertainty. Probability theory provides the only coherent logical foundation for such reasoning.'
11. A. Roth, 'Safety in Numbers? Deciding When DNA Alone is Enough to Convict' (2010) 85 NYU L Rev 1130 at 1162 quoting S. Cole and R. Diosa-Vila, 'CSI and Its Effects:Media, Juries, and the Burden of Proof' (2007) 41 New Eng L Rev 435-468
12. Articles rejecting the claimof forensic science evidence to uniqueness and individualization e.g. S. Cole, 'Forensic without uniqueness, conclusions without individualization: The new epistemology of forensic identification' (2009) 8 Law, Probability Risk 233
13. M. J. Saks and J.Koehler, The Individualization Fallacy in Forensic Science Evidence, (2008) 61 Vand L Rev 199
14. D. Kaye, 'Probability, Individualization and Uniqueness in Forensic Science Evidence' (200975 Brook L Rev 1163
15. The potential for problems in the chain of custody (i.e. continuity), laboratory and interpretational errors are not included in these estimates. See e.g. W. Thompson, 'The Potential for Error in ForensicDNATesting (andHowThatComplicates theUse of DNA Databases for Criminal Identification)' (2008) www.gene-watch.org
16. In Australia it is only the failure to explain matters peculiarly within the accused's knowledge that can be used by the jury, and then only to exclude doubts that might otherwise arise fromspeculating about that knowledge. See Azzopardi v R (2001) 205 CLR 50.
17. Psychological research endorsing the general use of this heuristic includes R. Hastie, 'Juror Decision-Making Models: The Generalisation Gap' (1981) 89 Psychology Bull 246, 251, and 'Evidence Evaluation in Complex Decision Making' (1986) 51 J. Personality and Soc. Psychology 242-244
18. J. Schklar and S. Diamond, 'Juror reactions to DNA evidence: Errors and expectancies' (1999) 23 Law & Human Behavior 159
19. D. Nance and S. Morris, 'Juror understanding of DNA evidence: An empirical assessment of presentation formats for trace evidence with a relatively small random-match probability' (2005) 34 J Legal Studies 395
20. J. Koehler, 'The Psychology of Numbers in the Courtroom: How to Make DNA-Match Statistics Seem Impressive or Insufficient' (2001) 74 Cal L Rev 1299-1300
21. Where Koehler concludes that: 'research indicates that people think heuristically rather than probabilistically. That is, when presented with quantitative information, we do not perform algebraic computations and arrive at solutions by using tenets of logic and probability theory. Instead, we evaluate quantitative evidence via mental shortcuts and other rules of thumb. In the case of DNA evidence, the ease with which we can imagine scenarios or examples of a match other than the suspect may be the heuristic of choice.' See also K. Martire, R. Kemp and B. Newell, 'The psychology of interpreting expert evaluative opinions', paper presented at the Impressions and Expressions conference, Sydney December 2011.
22. R. Burns, The Death of the American Trial (University of Chicago Press, 2009).
23. G.Harman, 'The Inference to the Best Explanation' (1965) 74 The Philosophical Rev 88
24. R.Allen, 'TheNature of Juridical Proof' (1991) 13 Cardozo L. R. 373
25. M. Pardo and R. Allen, 'Juridical Proof and the Best Explanation' (2008) 27 Law & Philosophy 223.
26. J. Cohen, The Probable and the Provable (Oxford University Press, Oxford, 1977).
27. We accept that some types of scientific inquiries (e.g. some areas of theoretical physics) may not be readily susceptible to experimental research. Such constraints are inapplicable to the vast majority of the forensic sciences. Revealingly, the reliability of many types of forensic science, particularly those involving subjective comparisons and pattern matching, remains uncertain. See e.g. National Research Council of the National Academy of Science, Strengthening Forensic Science in the United States: A Path Forward (Washington, DC: National Academies Press, 2009)
28. M. Saks and J. Koehler, 'The coming paradigm shift in forensic identification science' (2005) 309 Science 892
29. M. Saks and D. Faigman, 'Failed forensics: How forensic science lost its way and how it might yet find it' (2008) 4 Annual Rev Law & Social Sci 149.
30. The effectiveness of these adversarial protections are strongly doubted by empirical research. For an overview see G. Edmond and A. Roberts, 'Principles of evidence law and their implications for forensic science and medicine, (2011) 33 Sydney L Rev 359, and, more generally, B. Garrett, Convicting the innocent: Where criminal prosecutions go wrong (Harvard University Press, 2011). See also Law Commission of England andWales, Expert Evidence in Criminal Proceedings in England and Wales (HMSO, 2011) at 20-21
31. Atkins and Atkins [2009] EWAC Crim 1876
32. Otway v R [2011] EWCA Crim 3 (gait analysis). For criticism see G. Edmond, R. Kemp, G. Porter, D. Hamer, M. Burton, K. Biber and M. San Roque, 'Atkins v The Emperor: The 'cautious' use of unreliable 'expert' opinion' (2010) 14
33. This consensus was not easily achieved, see J. Aronson, GeneticWitness: Science, Law, and Controversy in theMaking of DNA Profiling (Rutgers University Press, 2007
34. See for example in Australia: R v Karger [2002] SASC 294 at [148]-[150] (Gray J) and Forbes v The Queen ACTCA 10 at [29], [40]2009
35. [2010] HCATrans 120 and in England and Wales: R v T [2010] EWCA Crim 2439 at 88-91
36. [2010] EWCA Crim 2439
37. [2009] EWCA Crim 1876.
38. [2010] EWCA Crim 2439 at [93]-[94]. In Atkins the expert's opinion was expressed in terms from a graded series-also used in R v T-but the use of the particular terms was based on non-systematic experience rather than empirical study or statistical information drawn from a relevant dataset or database. For criticism see G. Edmond, R. Kemp, G. Porter, D. Hamer, M. Burton, K. Biber andM. San Roque, 'Atkins v The Emperor: The 'cautious' use of unreliable 'expert' opinion' (2010) 14E& P 146.
39. [2011] EWCA Crim 3
40. Where such a conclusion is obvious such 'supplementary' opinions may be legally irrelevant, that is, without genuine assistance to the jury.
41. See references in n 23 above
42. See R v T [2010] EWCA Crim 2439 at [31], [54], [56], [58], [60].
43. M. Lynch, S. Cole, R. McNally, K. Jordan, Truth Machine: The contentious history of DNA fingerprinting (University of Chicago Press, 2008) 207-219.
44. This much greater degree of likelihood can be seen in the figures referred to in R v T at [31] and advocated by forensic scientists as appropriate benchmarks underlying verbal expressions of likelihood. The scale's lowest supporting point is 'weak or limited support' which means it is up to 10 times more likely the evidence would exist if the prosecution's contentions are true, 'moderate support' 10 to 100 times more likely, 'moderately strong support', 100 to 1000 times more likely, 'strong support' 1000 to 10000 times more likely, 'very strong support' 10 000 to 10 00 000 times more likely, 'extremely strong support' greater than 10 00 000 times more likely. Once revealed to explain the verbally expressed likelihood ratio these figures may become irresistibly compelling to a jury. For an example of a case where such figures were revealed to a jury see Forbes v The Queen ACTCA 10.2009
45. [2010] SASCFC 82 at [94]-[96].
46. And here, in a case dependant upon DNA evidence, the non-trivial issues of handling and laboratory errorsmight also have a role to play. See e.g. F.Vincent, Report: Inquiry into the Circumstances that Led to the Conviction of Mr Farah Abdulkadir Jama (Victorian Government Printer, 2010
47. C.f. approach by Sulan J in R v CarrollSASC 156 at [59].2010
48. The forensic scientists suggest that '9) It is regrettable that the judgement confuses the Bayesian approach with the use of Bayes' Theorem. The Bayesian approach does not necessarily involve the use of Bayes' Theorem.' The problem is howelse can the evidential effect of a likelihood ratio be computed? One can explain the Theorem in terms of simpler logic but it is much more convenient to use the formula to calculate evidential effec
49. A. Ligertwood, 'Can DNA Evidence Alone Convict an Accused?' (2011) 33 Sydney L Rev 487.
50. We recognize that this is an empirical issue, though one not particularly susceptible to investigation or analysis in the ecology of the trial