Journal Published Online: 01 May 2001
Volume 47, Issue 3

Interpreting Small Quantities of DNA: the Hierarchy of Propositions and the Use of Bayesian Networks



The dramatic increase in the sensitivity of DNA profiling systems that has occurred over recent years has led to the need to address a wider range of interpretational problems in forensic science. The issues surrounding questions of the kind “whose DNA is this?” have been the subject of considerable controversy but now it is clear that the emphasis is shifting to questions of the kind “how did this DNA get here?” Such issues are discussed in this paper and new insights are provided by two particular recent developments. First, the notion of the “hierarchy of propositions” that has arisen from a project called Case Assessment and Interpretation (CAI) that has been running in the British Forensic Science Service (FSS). Second, a technique for drawing inferences in the face of many interacting considerations, known as “Bayesian networks”— or “Bayes' nets“ for short—that has been the subject of an earlier paper in this journal (1). The discussion is carried out by means of case studies, based on actual cases. It is clear that, whereas the inference in relation to the source of the DNA in a crime sample might be overwhelmingly strong, the inference in relation to the propositions that a jury must consider relating to the identity of the actual offender may be much more tentative.

Author Information

Evett, IW
The Forensic Science Service, London
Gill, PD
The Forensic Science Service, Solihull
Jackson, G
The Forensic Science Service, Chorley
Whitaker, J
The Forensic Science Service, Solihull
Champod, C
The Forensic Science Service, Solihull
Pages: 11
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Stock #: JFS15291J
ISSN: 0022-1198
DOI: 10.1520/JFS15291J