Old Habits Die Hard: Precedent, Psychology, and the Admissibility of Forensic Evidence

Forensic evidence, long considered a cornerstone of criminal justice, has faced increasing scrutiny as recent studies and reports expose significant flaws in its scientific foundation. Techniques such as latent fingerprint analysis, microscopic hair comparison, and ballistics matching, which had been widely accepted for decades, are now being challenged for their lack of empirical validation. Yet, despite the growing acknowledgement of widespread issues affecting the reliability and validity of many types of forensic evidence, there are surprisingly few successful challenges to the admissibility of this type of forensic evidence, and, when the evidence is challenged, it is often found to be admissible. In the United States, Daubert and Rule 702 mandate that expert evidence be based on reliable principles and methods, but many courts have failed to rigorously apply these standards, often deferring to precedent rather than conducting a thorough analysis of the scientific validity of forensic techniques. This article argues that cognitive biases play a significant role in the US judicial system’s continued acceptance of unreliable forensic evidence. In particular, judges may rely on precedent as a heuristic – or cognitive shortcut – to admit unreliable forensic evidence, even in the face of new scientific evidence challenging the validity of that evidence. In this way, what appears to be deference to precedent may instead be the impact of various cognitive biases on the judge’s decision making. The discussion also considers how the bias blind spot contributes to judges’ reluctance to reject longstanding, but scientifically flawed, forensic techniques. Notwithstanding these challenges, judicial education on scientific standards, greater diversity on the bench, and a heightened awareness of cognitive biases and debiasing strategies could help mitigate these issues and promote more rigorous evaluation of forensic evidence in the courtroom.