Bloodstain pattern analysis: Does experience equate to expertise?

Alexandra Bettison; Matt N Krosch; Janet Chaseling; Kirsty Wright

doi:10.1111/1556-4029.14661

Bloodstain pattern analysis: Does experience equate to expertise?

J Forensic Sci. 2021 May;66(3):866-878. doi: 10.1111/1556-4029.14661. Epub 2021 Jan 4.

Authors

Alexandra Bettison¹, Matt N Krosch², Janet Chaseling³, Kirsty Wright⁴

Affiliations

¹ Scientific Section, Forensic Services Group, Queensland Police Service, Coomera, QLD, Australia.
² Quality Management Section, Forensic Services Group, Queensland Police Service, Brisbane, QLD, Australia.
³ School of Environment and Sciences, Griffith University, Nathan, QLD, Australia.
⁴ Centre for Genomics and Personalised Health, Genomics Research Centre, School of Biomedical Sciences, Institute of Health & Biomedical Innovation, Queensland University of Technology, Kelvin Grove, QLD, Australia.

PMID: 33394513
DOI: 10.1111/1556-4029.14661

Abstract

Bloodstain pattern analysis (BPA) has long been accepted by courts as an area of expertise; however, that position has recently been challenged. The discipline has been criticized for limited empirical research into practitioner determination error rates and whether determinations require specialized knowledge/expertise, including whether practitioner experience level influences accuracy. This study attempted to address these knowledge gaps as they relate to bloodstain pattern recognition. The aims were twofold: to establish whether practitioners would outperform lay non-practitioners, and whether practitioner experience influenced accuracy and error in determinations. Comparisons of practitioner responses under three scenarios (forced, casework, and definitive) were also made to assess conservatism/certainty in pattern recognition. Participants (both BPA practitioners and non-practitioners) analyzed photographs of bloodstain patterns and made determinations of the broad bloodstain category and specific bloodstain pattern type. When forced to provide only a single response, practitioners identified bloodstain categories and patterns significantly more accurately than non-practitioners (p = 0.0001, p < 0.00001, respectively). Practitioner accuracy in bloodstain pattern recognition was positively associated with experience level (p = 0.0429) and this was consistent regardless of response scenario. Although no significant difference in practitioner accuracy was observed across response scenarios, practitioner conservatism/certainty varied significantly among the broad bloodstain category and specific pattern types. Overall, these results support bloodstain pattern recognition as an area of expertise and that practitioner experience positively influences accuracy. Based on these results, a series of recommendations were proposed aimed at further improving practices within the discipline to maximize accuracy and reliability of BPA evidence.

Keywords: accuracy; error; experience; opinion evidence; pattern classification; pattern recognition; reliability; training.