Perceptions and Cognitive Bias in Decomposition Scoring Methods in Forensic Anthropology

There is increasing recognition within the forensic science community that human examiners are prone to biases that may affect the accuracy and precision of conclusions. The analysis of decomposition to estimate the postmortem interval (PMI) is one of the important functions of forensic anthropologists, yet analytical methods that rely on the judgment of human observers, such as assessing PMI from decomposition, may be vulnerable to cognitive bias, leading to inaccurate results. No studies to date have examined the effects of cognitive bias on decomposition scoring methods. The goal of this dissertation is to understand the role of the cognitive factors of mood and motivation on the analysis of decomposition characteristics both in field and photograph contexts. Fifty undergraduate research assistants with the University of Tennessee’s Forensic Anthropology Center assessed decomposition from 10 donated individuals over several months utilizing the Total Body Score method. Four graduate students who had extensive knowledge and experience with decomposition served as experts with which to compare the accuracy of observers’ TBS values. Observers also completed two psychological measures aimed at assessing their motivations (Intrinsic Motivation Inventory) and mood (Positive and Negative Affect Schedule) at the time of scoring. It was expected that observers and experts would differ in both the field and photograph contexts and that mood and motivation factors would be predictive of TBS values. Hierarchical random intercept multiple regression models were conducted to assess the relationship between these measures of cognition and observers’ TBS scores. Observers and experts only differed in the field context possibly due to biasing contextual information regarding the placement date of the donors. No differences were found in the photograph contexts because contextual information was not available to observers. Observers in the field context were motivated by their perceived performance, how nervous or pressured they felt while completing the task, and the perceived difficulty of the task itself. Mood only played a small role in the photograph context where negative mood influenced scoring decisions. This study has implications for the application of TBS to longitudinal research conducted at outdoor decomposition facilities as well as to cross-sectional casework