The Forensic Confirmation Bias: A Comparison Between Experts and Novices

A large body of research has described the influence of context information on forensic decision-making. In this study, we examined the effect of context information on the search for and selection of traces by students (N = 36) and crime scene investigators (N = 58). Participants investigated an ambiguous mock crime scene and received prior information indicating suicide, a violent death or no information. Participants described their impression of the scene and wrote down which traces they wanted to secure. Results showed that con- text information impacted first impression of the scene and crime scene behavior, namely number of traces secured. Participants in the murder condition secured most traces. Furthermore, the students secured more crime-related traces. Students were more confident in their first impres- sion. This study does not indicate that experts outperform novices. We therefore argue for proper training on cognitive processes as an integral part of all forensic education.

It is impossible to secure every item and trace at a crime scene. Therefore, crime scene investigators have to make decisions about the relevance of the available physical evidence on the spot. These decisions can be based both on the impression of the crime scene itself and on contextual information that is provided, such as investigative leads or witness statements. Hence, contextual information is likely to influence behavior of investigators at the crime scene. The influence of expectancy effects and contextual bias on decision‐making has been described in a broad range of forensic disciplines, see 1, for an overview.

In recent years, there has been increased attention for cognitive bias in the forensic science community worldwide 2-4. Also, an increasing body of research focuses on the influence of bias on forensic comparisons in laboratories 5-7. Despite the efforts of various forensic sciences institutes and governments to create awareness of bias, a recent study 8 demonstrates that forensic experts consider bias as something that mainly concerns others, not themselves. Therefore, more research on the influence of the forensic confirmation bias is on the field of practice is necessary. In a previous study, we explored the influence of contextual information on the interpretation of a crime scene. Results demonstrated that experienced crime scene investigators can also be prone to bias and that prior information can help with the interpretation of the scene when it is correct, but can cause the crime scene to be interpreted wrongfully when it is incorrect 9.