title: Bloodstain pattern classification: Accuracy, effect of contextual information and the role of analyst characteristics.
abstract: It is becoming increasingly apparent that contextual information can exert a considerable influence on decisions about forensic evidence. Here, we explored accuracy and contextual influence in bloodstain pattern classification, and how these variables might relate to analyst characteristics. Thirty-nine bloodstain pattern analysts with varying degrees of experience each completed measures of compliance, decision-making style, and need for closure. Analysts then examined a bloodstain pattern without any additional contextual information, and allocated votes to listed pattern types according to favoured and less favoured classifications. Next, if they believed it would assist with their classification, analysts could request items of contextual information - from commonly encountered sources of information in bloodstain pattern analysis - and update their vote allocation. We calculated a shift score for each item of contextual information based on vote reallocation. Almost all forms of contextual information influenced decision-making, with medical findings leading to the highest shift scores. Although there was a small positive association between shift scores and the degree to which analysts displayed an intuitive decision-making style, shift scores did not vary meaningfully as a function of experience or the other characteristics measured. Almost all of the erroneous classifications were made by novice analysts.
authors.affiliation: Department of Psychology, University of Otago, PO Box 56, Dunedin 9054, New Zealand; The Institute of Environmental Science and Research (ESR), Christchurch Science Centre, PO Box 29181, Christchurch 8540, New Zealand. Electronic address: nosborne@psy.otago.ac.nz.
authors.forename: Nikola K P
authors.initials: NK
authors.lastname: Osborne
authors.affiliation: The Institute of Environmental Science and Research (ESR), Christchurch Science Centre, PO Box 29181, Christchurch 8540, New Zealand. Electronic address: michael.taylor@esr.cri.nz.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Taylor
authors.affiliation: Department of Women's and Children's Health, University of Otago, PO Box 56, Dunedin 9054, New Zealand. Electronic address: matthew.healey@otago.ac.nz.
authors.forename: Matthew
authors.initials: M
authors.lastname: Healey
authors.affiliation: Department of Psychology, University of Otago, PO Box 56, Dunedin 9054, New Zealand. Electronic address: rachelz@psy.otago.ac.nz.
authors.forename: Rachel
authors.initials: R
authors.lastname: Zajac
mesh_terms: D001801:Blood Stains; D044707:Forensic Sciences; D006801:Humans; D015588:Observer Variation; D010364:Pattern Recognition, Visual; D011361:Professional Competence
keywords: Bayesian analysis; Bloodstain pattern analysis; Cognitive science; Contextual bias; Individual characteristics