The Individualization Fallacy in Forensic Science Evidence

Abstract

Forensic identification science involves two fundamental steps. The first step is to compare a questioned item of evidence to an exemplar from a known source and judge whether they appear so alike that they can be said to match. The second step is to assess the meaning of that reported match: What is the probability that the questioned and the known originated from the same source? Part II of this Essay explains what we mean by the term 'individualization fallacy' and describes the origins of individualization in criminalistics. Part III critically examines the arguments offered in support of the individualization hypothesis. This Part also addresses the second step in forensic identification: What inferences can be drawn from a forensic scientist's conclusion that an exemplar (such as a partial fingerprint, handwriting sample, or tireprint) matches a known source? Forensic scientists across a broad array of sub-specialties long have maintained that such a finding is synonymous with a conclusion that the exemplar marking is produced by the known source. Part IV gives a historical account of scientists who have recognized the problem of individualization in forensic science. Part V offers suggestions for ways to improve the scientific foundation of identification in criminalistics. Finally, Part VI concludes that forensic scientists must provide sound evidence for their conclusions and should avoid exaggerating their results.