Practical Guide for the Formulation of Propositions in the Bayesian Approach to DNA Evidence Interpretation in an Adversarial Environment

• NCJ Number: 249398
• Author(s): Simone Gittelson, Tim Kalafut, Steven Myers, Duncan Taylor, Tacha Hicks, Franco Taroni, Ian W. Evett, Jo-Anne Bright, John Buckleton
• Date Published: January 2016
• Length: 10 pages
• Agencies: NIJ-Sponsored
• Award: Population Genetic Issues for Forensic DNA Profiles

Annotation

This note explores the issue of proposition setting in an adversarial environment by a series of examples.

Abstract

The interpretation of complex DNA profiles is facilitated by a Bayesian approach. This approach requires the development of a pair of propositions, one aligned to the prosecution case and one to the defense case. A set of guidelines generalize how to formulate propositions when there is a single person of interest and when there are multiple individuals of interest. Additional explanations cover how to handle multiple defense propositions, relatives, and the transition from sub-source level to activity-level propositions. The propositions depend on case information and the allegations of each of the parties. The prosecution proposition is usually known. The authors suggest that a sensible proposition is selected for the defense that is consistent with their stance, if available, and consistent with a realistic defense if their position is not known. (Publisher abstract modified)