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Forensic science, probabilities and the law - scientific evidence at trial


Research objectives and content
Forensic science suggests itself as a case-study as there is a degree of consensus that forensic scientific evidence should be thought about in probabilistic terms (Aitken, 1995; Robertson & Vignaux, 1995a; Weir (ed.), (1995), but when we surveyed the field - as we did during the first part of the European Community project "Probabilistic Reasoning in the Law" - it appeared to us to be confused.
In fact, some expert witnesses, such as fingerprints, tool marks, firearms and shoe prints experts, make categorical statements that two impressions are from the same source; some expert witnesses, such as glass, fibers and hair experts, would only say that a sample could have come from a particular source and then give some apparently straightforward statistics about the frequency of the trace of that type; some types of evidence, such as DNA, involve complex statistical arguments which may be misinterpreted by the court and confuse the experts.
Jurists seemed equally confused, because experts usurp the decision-making role of judges or members of juries when they express results in forms like the one used in paternity cases; forensic evidence has - by its nature - a close link to statistical assessment, but some courts do not accept such a form of evidence, believing that members of the jury could be misled by it. It seems important to point out both the lack of communication between the forensic and judicial worlds and the misinterpretation of the value of statistical evidence when, routinely, such evidence supports a scientific argument in the adversarial system of the trial process. Therefore, we believe that the appropriate interpretative procedures which have been developed for the assistance of both jurists and scientists during the second part of the current granted research should be applied practically to ease communication between the forensic and judicial world and to aid in the correct interpretation of statistical evidence. These aspects are the aim of our new project.
Training content (objective, benefit and expected impact)
The proposal would be to increase our knowledge with reference to measures of uncertainty associated with the presentation and understanding of scientific evidence by students and practitioners outside Scotland. The study will allow us to define better the problem in some European and extra-European countries and to structure a natural consequence of the results shown in the previous granted project and of the expected results of this first part described above. Suitable interpretative procedures will be proposed both through a new proficiency test addressed to forensic science laboratories (previously contacted during the first grant and during the current proposal) and through evidence interpretation courses, to be given to audiences containing a mix of lawyers and forensic scientists. with the principal aim of assisting scientist and jurists to increase their knowledge in the management of probabilities linked to scientific evidence.
Links with industry / industrial relevance (22)
This project is designed to be accepted by both forensic scientists and jurists so that each will better understand the other and so that they will be better equipped to work together to explain the evidence to the court.

Funding Scheme

RGI - Research grants (individual fellowships)


Mayfield Road, James Clerk Maxwell Bdg., Kings Bui
EH9 3JZ Edinburgh
United Kingdom

Participants (1)

Not available