The panel will discuss, from an interdisciplinary standpoint, to what extent can we quantify the uncertainty of forensic reports, and whether it is possible to agree on a European standard for reporting uncertainty in court.
During the last decade European courts have moved in opposite directions in the way they deal with the uncertainty of forensic evidence. To what extent a piece of forensic evidence provides proof of guilt or innocence? How reliable is the science behind forensic analyses? Whereas countries like Sweden have tried to quantify and standardize the uncertainty of each forensic report, so that it can be reliably communicated in court, Spain has chosen to neglect forensic uncertainty and present evidence in court in terms of categorical statements, without giving the defendant the option to confront and question the forensic expert. In this session we want to bring together forensic practitioners, sociologists and philosophers of science to discuss which way is best to face forensic uncertainty.
Col. Jose Juan Lucena, Head, Escuela de Especialización of the Spanish Guardia Civil (military police)
Dr. Corinna Kruse, Technology and Social Change, Linköping University
Dr. Marion Vorms (Psychology, Birbeck College)
Prof. Annouk Barberousse, Dr. Isabelle Drouet (Philosophy, Paris IV)
Dr. David Teira (Philosophy, UNED), chair and discussant
Lucena will present, from a practitioner's perspective, how the
uncertainty of forensic reports is evaluated in Europe. Kruse, from a
STS standpoint, will present her fieldwork with the pioneering Swedish
initiative of standardizing forensic uncertainty with Bayesian
statistics. Vorms would explore, through experimental evidence, what
forensic "reasonable doubt" may mean in various situations of
decision-making under uncertainty. Barberousse and Drouet will discuss,
from a philosophy of science standpoint, the sources of the credibility
of forensic experts.
This track is closed to new paper proposals.
Standardizing and Communicating Forensic Uncertainty with Bayesian Statistics
The paper discusses how forensic scientists in the Swedish criminal justice system use a Bayesian approach to make uncertainty quantifyable, manageable, and communicable.
Based on ethnographic fieldwork, I will discuss how forensic scientists in the Swedish criminal justice system use a particular quantitative approach to evaluating forensic laboratory results, the Bayesian approach, as a means of quantifying uncertainty and communicating it to judges, prosecutors, and defense lawyers. Their use of the Bayesian approach brings about a particular type of intersubjectivity; in order to make different types of forensic evidence commensurable and combinable, quantifications must be consistent across forensic specializations, which brings about a transparency based on shared understandings and practices. Finally, the Bayesian approach is also a means of distributing responsibility between the laboratory and the court.
Reasonable doubt and the use of Bayesian reasoning in expert witness reports
This paper will confront two aspects of the use of probabilities in court, namely the use of Bayesian reasoning in the assessment of the weight of forensic evidence, and the ‘reasonable doubt’ standard of proof, which can prima facie be interpreted as referring to a probabilistic threshold.
Interdisciplinary efforts are deployed in the UK to promote Bayesian reasoning in the assessment and communication of the weight of forensic evidence (against some judges' attempts at ruling out statistics from the court), and to make tools for analysing arguments (eg Bayesian networks, Fenton et al. 2012, 2013a) accessible to judges and juries. Indeed, simply appealing to probabilities is not sufficient to avoid miscarriages of justice. As Fenton et al. (2013b) show, likelihood ratios can be used to assess the probative value of evidence under certain circumstances only — namely, that the prosecution and defence hypotheses be exhaustive and mutually exclusive, and at the offence level, rather than at the source or activity levels (Cook et al. 1998).
I will draw on this proposal, adopting the perspective of the jurors, who are instructed to estimate whether guilt was proven 'beyond a reasonable doubt'. This may prima facie indicate that the evidence presented in court should support the hypothesis of guilt to a certain degree — that a certain probabilistic threshold has to be met — for the defendant to be convicted. However, depending on how the defence and prosecution hypotheses are formulated and argued for (scenarios do not reduce to "he is guilty" / "he is not guilty"), and on their logical relationships, the evaluation of the probability of guilt — and of its robustness and resilience to potentially different structurations of the hypotheses space — may vary. This, I will argue, should be taken into account in any effort to clarify the 'reasonable doubt' standard.
The credibility of scientific evidence
Why has credibility not appeared as an important question concerning science? In other words, why credibility questions are easier to answer concerning scientific investigation than inin the case of criminal or judicial investigation?
In his 2004 book, Schum considers that, relative to a given hypothesis, evidence has three features (or, in his terminology, "credentials"): credibility, relevance and probative force. Analyses of relevance and probative force can be found in philosophy of science, since they are (more or less) the objects of theories of confirmation, qualitative and quantitative respectively. But it seems that philosophers of science have not been much interested in credibility. Assuming that this is not due to mere negligence, the question arises why credibility has not appeared as an important question concerning science or, in other words, why credibility questions are easier to answer concerning scientific investigation than in general case or, more specifically, than in the case of criminal or judicial investigation. This question is mainly an empirical one: what are the features of the institutional or social organization of science that make credibility a non-issue or an easy question? It should be interesting to envisage the question dynamically: are recent changes in the organisation or social features of science such that credibility issues are becoming more of an issue? is it the case that controversies recently arouse that show that credibility tends to become an issue about science (both in science and in society)? Of course, all this does not deal with forensic science per se, but rather about what looking at criminal investigation and work dealing with it may tell us about science.
This track is closed to new paper proposals.