A local seminar presented by Dr Colin Aitken, School of Mathematics and Joseph Bell Centre for Forensic Statistics and Legal Reasoning, University of Edinburgh
Thursday 26th April 2012, 12.30pm-2.00pm
University of Edinburgh, Room 1.11, Main Library, 30 George Square, Edinburgh EH8 9LJ
The use of graphs to illustrate the structure of a criminal investigation is not new, being first introduced by Wigmore in 1937 with tree diagrams. A more recent probabilistic approach to the evaluation of evidence us- ing graphs will be described. Pieces of evidence and propositions are represented by nodes and associations between pieces of evidence and propositions are represented by lines joining nodes. The strengths of the associations are measured by probabilities. The technique will be illustrated by an example in offender profiling motivated by an investigation of sexually motivated child murders in the 1990’s and, more recently, the case of R v T (2010, EWCA Crim 2439).
This graph describes a relationship between evidence and a proposition. The proposition can take one of two values: a defendant is guilty or is innocent. The directed edge illustrates the relationship of evidence with this proposition and there is information about the probability of the evidence if the defendant is guilty and the prob- ability of the evidence if the defendant is innocent. Rules of probability can be used to reverse the inference to derive probabilities for guilt and for innocence given the evidence and hence evidential value. The idea can be applied to graphs with many nodes and many edges.
Places are limited
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