Evaluating findings of fibre comparisons in forensic science. Part 1: Considering the occurrence and background

Findings from forensic fibre analysis need to be interpreted with respect to relevant competing propositions and case contextual information. This requires the attribution of probabilities to certain factors which typically include the occurrence for source level propositions, as well as transfer, persistence, recovery, and background, in addition to occurrence, for activity level ones. On top of applying their expertise, practitioners often turn to published literature to aid in this process. Effectively, published research offers a wealth of applicable knowledge, from frequency data to insights on the effects that certain variables can have. Given the polyvalent and ubiquitous nature of fibres, not all articles will be equally applicable to a given case. This, combined with the wealth of available studies means careful selection of relevant literature is essential on a case-by-case basis. Schnegg et al. [1,2] had previously published a set of literature studies in French aimed at helping in the process. This set of papers in English is meant to be complimentary to that work. It summarizes the main consensus on the aforementioned factors that need to be attributed during an evaluation. It also provides useful overarching data that can be applied in assigning their relevant probabilities and points the reader towards the source of the information for further reading. The current paper is the first of a series and focuses on the background and occurrence parameters.