Expressing evaluative opinions: a position statement

Colin Aitken, Charles E. H. Berger, John S. Buckleton, Christophe Champod, James Curran, A. P. Dawid, Ian W. Evett, Peter Gill, Joaquin Gonzalez-Rodriguez, Graham Jackson, Ate Kloosterman, Tina Lovelock, David Lucy, Pierre Margot, Louise McKenna, Didier Meuwly, Cedric Neumann, Niamh Nic Daeid, Anders Nordgaard, Roberto Puch-Solis & 11 others Birgitta Rasmusson, Mike Redmayne, Paul Roberts, Bernard Robertson, Claude Roux, Marjan J. Sjerps, Franco Taroni, Tjark Tjin-A-Tsoi, G. A. Vignaux, Sheila M. Willis, Grzegorz Zadora

Research output: Contribution to journalEditorial

65 Citations (Scopus)

Abstract

The judgment of the Court of Appeal in R v T [1] raises several issues relating to the evaluation of scientific evidence that, we believe, require a response.
We, the undersigned, oppose any response to the judgment that would result in a movement away from the use of logical methods for evidence evaluation. A paper in this issue of the Journal [2] re-iterates logical principles of evidence interpretation that are accepted by a broad range of those who have an interest in forensic reasoning. The divergence between those principles of interpretation and the apparent implications of the R v T ruling are epitomised by the following issues that represent our collective position with regard to the evaluation of evidence within the context of a criminal trial.
1) The interpretation of scientific evidence invokes reasoning in the face of uncertainty. Probability theory provides the only coherent logical foundation for such reasoning.
2) To form an evaluative opinion from a set of observations, it is necessary for the forensic scientist to consider those observations in the light of propositions that represent the positions of the different participants in the legal process. In a criminal trial, the propositions will represent the positions of prosecution and defence, respectively.
3) It is necessary for the scientist to consider the probability of the observations given each of the stated propositions. Not only is it not appropriate for the scientist to consider the probability of the proposition given the observations, there is a danger that in doing so the jury will be misled.
4) The ratio of the probability of the observations given the prosecution proposition to the probability of the observations given the defence proposition, which is known as the likelihood ratio, provides the most appropriate foundation for assisting the court in establishing the weight that should be assigned to those observations.
5) A verbal scale based on the notion of the likelihood ratio is the most appropriate basis for communication of an evaluative expert opinion to the court. It can be phrased in terms of support for one of a pair of clearly stated propositions.
6) Not only are phrases such as “could have come from” or “is consistent with” ineffective for communicating the scientist's opinion with regard to the weight that should be assigned to a set of observations, but there is also a danger that they may be misleading.
7) Probabilities should be informed by data, knowledge and experience. All data collections are imperfect and incomplete and it necessarily follows that different experts might legitimately assign different probabilities to the same set of observations.
8) The logical approach to evaluating evidence implicit in the foregoing points has come to be known as the “Bayesian approach”. The ideas behind this approach are not novel. Indeed, they were first applied to resolving a serious miscarriage of justice in the Dreyfus case in 1908.
9) It is regrettable that the judgment confuses the Bayesian approach with the use of Bayes' Theorem. The Bayesian approach does not necessarily involve the use of Bayes' Theorem.
10) While we are fully in agreement with the principle of disclosure, candour and full disclosure in court can undermine comprehensibility when scientific evaluations involve technicalities. Pre-trial hearings should be used to explore the basis of expert opinions and to resolve if possible any differences between experts.

LanguageEnglish
Pages1-2
Number of pages2
JournalScience and Justice
Volume51
Issue number1
Early online date5 Feb 2011
DOIs
Publication statusPublished - Mar 2011

Fingerprint

Bayes Theorem
Disclosure
Expert Testimony
Probability Theory
Weights and Measures
Social Justice
Spontaneous Abortion
Hearing
Uncertainty
Communication

Keywords

  • expressing
  • evaluative opinions
  • position statement

Cite this

Aitken, C., Berger, C. E. H., Buckleton, J. S., Champod, C., Curran, J., Dawid, A. P., ... Zadora, G. (2011). Expressing evaluative opinions: a position statement. Science and Justice, 51(1), 1-2. https://doi.org/10.1016/j.scijus.2011.01.002
Aitken, Colin ; Berger, Charles E. H. ; Buckleton, John S. ; Champod, Christophe ; Curran, James ; Dawid, A. P. ; Evett, Ian W. ; Gill, Peter ; Gonzalez-Rodriguez, Joaquin ; Jackson, Graham ; Kloosterman, Ate ; Lovelock, Tina ; Lucy, David ; Margot, Pierre ; McKenna, Louise ; Meuwly, Didier ; Neumann, Cedric ; Daeid, Niamh Nic ; Nordgaard, Anders ; Puch-Solis, Roberto ; Rasmusson, Birgitta ; Redmayne, Mike ; Roberts, Paul ; Robertson, Bernard ; Roux, Claude ; Sjerps, Marjan J. ; Taroni, Franco ; Tjin-A-Tsoi, Tjark ; Vignaux, G. A. ; Willis, Sheila M. ; Zadora, Grzegorz. / Expressing evaluative opinions : a position statement. In: Science and Justice. 2011 ; Vol. 51, No. 1. pp. 1-2.
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Aitken, C, Berger, CEH, Buckleton, JS, Champod, C, Curran, J, Dawid, AP, Evett, IW, Gill, P, Gonzalez-Rodriguez, J, Jackson, G, Kloosterman, A, Lovelock, T, Lucy, D, Margot, P, McKenna, L, Meuwly, D, Neumann, C, Daeid, NN, Nordgaard, A, Puch-Solis, R, Rasmusson, B, Redmayne, M, Roberts, P, Robertson, B, Roux, C, Sjerps, MJ, Taroni, F, Tjin-A-Tsoi, T, Vignaux, GA, Willis, SM & Zadora, G 2011, 'Expressing evaluative opinions: a position statement' Science and Justice, vol. 51, no. 1, pp. 1-2. https://doi.org/10.1016/j.scijus.2011.01.002

Expressing evaluative opinions : a position statement. / Aitken, Colin; Berger, Charles E. H.; Buckleton, John S.; Champod, Christophe; Curran, James; Dawid, A. P.; Evett, Ian W.; Gill, Peter; Gonzalez-Rodriguez, Joaquin; Jackson, Graham; Kloosterman, Ate; Lovelock, Tina; Lucy, David; Margot, Pierre; McKenna, Louise; Meuwly, Didier; Neumann, Cedric; Daeid, Niamh Nic; Nordgaard, Anders; Puch-Solis, Roberto; Rasmusson, Birgitta; Redmayne, Mike; Roberts, Paul; Robertson, Bernard; Roux, Claude; Sjerps, Marjan J.; Taroni, Franco; Tjin-A-Tsoi, Tjark; Vignaux, G. A.; Willis, Sheila M.; Zadora, Grzegorz.

In: Science and Justice, Vol. 51, No. 1, 03.2011, p. 1-2.

Research output: Contribution to journalEditorial

TY - JOUR

T1 - Expressing evaluative opinions

T2 - Science and Justice

AU - Aitken, Colin

AU - Berger, Charles E. H.

AU - Buckleton, John S.

AU - Champod, Christophe

AU - Curran, James

AU - Dawid, A. P.

AU - Evett, Ian W.

AU - Gill, Peter

AU - Gonzalez-Rodriguez, Joaquin

AU - Jackson, Graham

AU - Kloosterman, Ate

AU - Lovelock, Tina

AU - Lucy, David

AU - Margot, Pierre

AU - McKenna, Louise

AU - Meuwly, Didier

AU - Neumann, Cedric

AU - Daeid, Niamh Nic

AU - Nordgaard, Anders

AU - Puch-Solis, Roberto

AU - Rasmusson, Birgitta

AU - Redmayne, Mike

AU - Roberts, Paul

AU - Robertson, Bernard

AU - Roux, Claude

AU - Sjerps, Marjan J.

AU - Taroni, Franco

AU - Tjin-A-Tsoi, Tjark

AU - Vignaux, G. A.

AU - Willis, Sheila M.

AU - Zadora, Grzegorz

PY - 2011/3

Y1 - 2011/3

N2 - The judgment of the Court of Appeal in R v T [1] raises several issues relating to the evaluation of scientific evidence that, we believe, require a response. We, the undersigned, oppose any response to the judgment that would result in a movement away from the use of logical methods for evidence evaluation. A paper in this issue of the Journal [2] re-iterates logical principles of evidence interpretation that are accepted by a broad range of those who have an interest in forensic reasoning. The divergence between those principles of interpretation and the apparent implications of the R v T ruling are epitomised by the following issues that represent our collective position with regard to the evaluation of evidence within the context of a criminal trial. 1) The interpretation of scientific evidence invokes reasoning in the face of uncertainty. Probability theory provides the only coherent logical foundation for such reasoning. 2) To form an evaluative opinion from a set of observations, it is necessary for the forensic scientist to consider those observations in the light of propositions that represent the positions of the different participants in the legal process. In a criminal trial, the propositions will represent the positions of prosecution and defence, respectively. 3) It is necessary for the scientist to consider the probability of the observations given each of the stated propositions. Not only is it not appropriate for the scientist to consider the probability of the proposition given the observations, there is a danger that in doing so the jury will be misled. 4) The ratio of the probability of the observations given the prosecution proposition to the probability of the observations given the defence proposition, which is known as the likelihood ratio, provides the most appropriate foundation for assisting the court in establishing the weight that should be assigned to those observations. 5) A verbal scale based on the notion of the likelihood ratio is the most appropriate basis for communication of an evaluative expert opinion to the court. It can be phrased in terms of support for one of a pair of clearly stated propositions. 6) Not only are phrases such as “could have come from” or “is consistent with” ineffective for communicating the scientist's opinion with regard to the weight that should be assigned to a set of observations, but there is also a danger that they may be misleading. 7) Probabilities should be informed by data, knowledge and experience. All data collections are imperfect and incomplete and it necessarily follows that different experts might legitimately assign different probabilities to the same set of observations. 8) The logical approach to evaluating evidence implicit in the foregoing points has come to be known as the “Bayesian approach”. The ideas behind this approach are not novel. Indeed, they were first applied to resolving a serious miscarriage of justice in the Dreyfus case in 1908. 9) It is regrettable that the judgment confuses the Bayesian approach with the use of Bayes' Theorem. The Bayesian approach does not necessarily involve the use of Bayes' Theorem. 10) While we are fully in agreement with the principle of disclosure, candour and full disclosure in court can undermine comprehensibility when scientific evaluations involve technicalities. Pre-trial hearings should be used to explore the basis of expert opinions and to resolve if possible any differences between experts.

AB - The judgment of the Court of Appeal in R v T [1] raises several issues relating to the evaluation of scientific evidence that, we believe, require a response. We, the undersigned, oppose any response to the judgment that would result in a movement away from the use of logical methods for evidence evaluation. A paper in this issue of the Journal [2] re-iterates logical principles of evidence interpretation that are accepted by a broad range of those who have an interest in forensic reasoning. The divergence between those principles of interpretation and the apparent implications of the R v T ruling are epitomised by the following issues that represent our collective position with regard to the evaluation of evidence within the context of a criminal trial. 1) The interpretation of scientific evidence invokes reasoning in the face of uncertainty. Probability theory provides the only coherent logical foundation for such reasoning. 2) To form an evaluative opinion from a set of observations, it is necessary for the forensic scientist to consider those observations in the light of propositions that represent the positions of the different participants in the legal process. In a criminal trial, the propositions will represent the positions of prosecution and defence, respectively. 3) It is necessary for the scientist to consider the probability of the observations given each of the stated propositions. Not only is it not appropriate for the scientist to consider the probability of the proposition given the observations, there is a danger that in doing so the jury will be misled. 4) The ratio of the probability of the observations given the prosecution proposition to the probability of the observations given the defence proposition, which is known as the likelihood ratio, provides the most appropriate foundation for assisting the court in establishing the weight that should be assigned to those observations. 5) A verbal scale based on the notion of the likelihood ratio is the most appropriate basis for communication of an evaluative expert opinion to the court. It can be phrased in terms of support for one of a pair of clearly stated propositions. 6) Not only are phrases such as “could have come from” or “is consistent with” ineffective for communicating the scientist's opinion with regard to the weight that should be assigned to a set of observations, but there is also a danger that they may be misleading. 7) Probabilities should be informed by data, knowledge and experience. All data collections are imperfect and incomplete and it necessarily follows that different experts might legitimately assign different probabilities to the same set of observations. 8) The logical approach to evaluating evidence implicit in the foregoing points has come to be known as the “Bayesian approach”. The ideas behind this approach are not novel. Indeed, they were first applied to resolving a serious miscarriage of justice in the Dreyfus case in 1908. 9) It is regrettable that the judgment confuses the Bayesian approach with the use of Bayes' Theorem. The Bayesian approach does not necessarily involve the use of Bayes' Theorem. 10) While we are fully in agreement with the principle of disclosure, candour and full disclosure in court can undermine comprehensibility when scientific evaluations involve technicalities. Pre-trial hearings should be used to explore the basis of expert opinions and to resolve if possible any differences between experts.

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KW - evaluative opinions

KW - position statement

U2 - 10.1016/j.scijus.2011.01.002

DO - 10.1016/j.scijus.2011.01.002

M3 - Editorial

VL - 51

SP - 1

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JO - Science and Justice

JF - Science and Justice

SN - 1355-0306

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Aitken C, Berger CEH, Buckleton JS, Champod C, Curran J, Dawid AP et al. Expressing evaluative opinions: a position statement. Science and Justice. 2011 Mar;51(1):1-2. https://doi.org/10.1016/j.scijus.2011.01.002