Theoretical and Empirical Investigation of Cognitive Bias in Nigerian Forensic Examiner Decision-Making

Cognitive bias in forensic examiner decision-making represents a fundamental threat to the objectivity of forensic science evidence, with documented influences including confirmation bias, contextual bias, and anchoring effects shown to systematically affect examiner conclusions. This doctoral study conducts a theoretical and empirical investigation of cognitive bias among forensic examiners in Nigerian public forensic laboratories. Drawing on cognitive psychology theory, judgment and decision-making frameworks, and the forensic science bias literature, the study develops a Nigeria-specific Forensic Examiner Bias Taxonomy. An experimental mixed-methods design was employed, conducting blinded experiments with 150 forensic examiners from across six geopolitical zones in which identical evidence sets were presented with varying contextual information to measure bias-induced conclusion divergence, supplemented by qualitative interviews with thirty examiners exploring subjective decision-making processes. The study evaluates the magnitude, prevalence, and examiner characteristic predictors of cognitive bias across fingerprint, tool mark, document, and trace evidence disciplines. Findings demonstrate statistically significant contextual bias effects across all disciplines, with fingerprint examiners showing the greatest susceptibility and trace evidence examiners the least. Contextual information provided by investigators produced conclusion reversals in seventeen percent of experimental trials. The study makes original theoretical contributions to the global forensic bias literature by contextualising bias mechanisms within Nigerian institutional and professional culture factors. Recommendations include the implementation of linear sequential unmasking procedures and blind verification protocols in Nigerian forensic laboratories. Keywords: cognitive bias, forensic examiners, decision-making, Nigeria, contextual bias.