Evaluating findings of fibre comparisons in forensic science. Part 2: Considering transfer, persistence, and recovery

After a forensic fibre analysis, the results need to be interpreted with respect to the relevant competing propositions and case context. The assignment of probabilities to parameters such as occurrence, background, transfer, persistence, and recovery, is indispensable to this process. This paper will summarise and consolidate the current body of knowledge on the subject of transfer, persistence, and recovery. These parameters are often grouped together due to their close relationship. Primarily they offer on explanation for the quantity of fibres that would be found on a relevant surface, and it is this quantity on which most evaluations are based. Crucially, for findings to be helpful, there often needs to be a distinction between the expected number of fibres found as a result of each competing proposition and the background. These three different processes are highly complex and have a variety of interacting elements that affect them. The consensus in the literature on these elements and how they influence these events are covered in this paper. This knowledge sheds light on the expected number of fibres as a result of the transfer, persistence, and recovery in the context of an activity. Finally, lists of published research are given, such that experts may select the relevant ones and consult them for further information. The objective is to assist experts in selecting relevant literature and adapting them for their specific needs on a case-by-case basis. Finally, the application of this data and information into practical probability assignment is demonstrated using an example.