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

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

The Probabilistic Genotyping Software STRmix: Utility and Evidence for its Validity

“…• Which, if any, of the known individuals may be reasonably assumed to be contributors (30)(31)(32),…”

“…• How to deal with multiple POIs (30,31), • How to deal with evidential items associated with neither the POI nor the victim (30,31).…”

“…Gittelson et al. discussed this concept more recently. Propositions are classified into four levels: offence, activity, source, and subsource.…”

“…Gittelson et al. suggested a requirement for interpretation:

Due attention must be paid to the position in the hierarchy of propositions that can be considered. This information must be effectively conveyed to the court to avoid the risk that an evaluation at one level is translated uncritically and without modification to evaluation at a higher level.

…”

“… Which, if any, of the known individuals may be reasonably assumed to be contributors , The number of contributors to the profile (discussed later in this paper) , How to deal with multiple POIs , How to deal with evidential items associated with neither the POI nor the victim . …”