Cognitive bias affecting forensic expert opinion

Author Lirieka Meintjes Van Der Walt and Adebola Olaborede

ISSN: 1996-2118
Affiliations: BJuris LLB (UPE) LLM (Rhodes) LLD (Leiden); Adjunct Professor of Law and Leader of the Law, Science and Justice Research Niche Area, University of Fort Hare.; LLB (Nigeria), LLM (Stellenbosch), LLD (UFH); Post-Doctoral Research Fellow, Law, Science and Justice Research Niche Area, University of Fort Hare.
Source: South African Journal of Criminal Justice, Volume 32 Issue 3, p. 324 – 356


The influence of bias in forensic expert opinion can create problems for the criminal justice system. Many research studies have shown that forensic experts can be susceptible to cognitive bias that influences their memory and reasoning and affects the objectivity of their opinion and decisions. This has contributed to the misidentifications and consequent wrongful convictions of innocent persons. This article examines bias that can affect the opinion offered by forensic experts in criminal trials and discusses the risk of bias in some forensic science disciplines, such as fingerprint examination, trace evidence, bullet comparison and DNA analysis. The article contends that different factors such as the quality and/or clarity of the forensic evidence, contextual case information and subjective interpretation of forensic analysis can exacerbate bias. Strategies recommended for mitigating bias include blind testing, blind verification, independent review, linear sequential unmasking (LSU) and the filler control method. The merits and demerits of these strategies are highlighted. The article also proposes certain cross-examination questions that could expose bias in forensic examination.