The Absence or Misuse of Statistics in Forensic Science as a Contributor to Wrongful Convictions: From Pattern Matching to Medical Opinions About Child Abuse

Abstract

The new scrutiny that has been applied to the forensic sciences since the emergence of DNA profiling as the gold standard three decades ago has identified numerous concerns about the absence of a solid scientific footing for most disciplines. This article examines one of the lesser-considered problems that afflicts virtually all of the pattern-matching (or "individualization") disciplines (largely apart from DNA), and even undermines the validity of other forensic disciplines like forensic pathology and medical determinations about child abuse, particularly Shaken Baby Syndrome/Abusive Head Trauma (SBS/AHT). That problem is the absence or misuse of statistics. This article begins by applying basic statistical principles to pattern-matching disciplines to demonstrate how those disciplines have historically hidden or failed to reckon with the probabilistic nature of their judgments, and how, when they have acknowledged the probabilistic nature of their claims, they have often botched the statistical analyses. The article then does a deeper dive into showing how those same deficiencies apply to medical opinions about child abuse, particularly SBS/AHT.

Keywords: Statistics, probabilities, forensic science, wrongful convictions, Bayes' Theorem, prosecutor's fallacy, shaken baby syndrome, abusive head trauma, microscopic hair analysis, likelihood ratio, relevance ratio

JEL Classification: K42: Illegal Behavior and the Enforcement of Law