Fall 2018

Certainty & Uncertainty in Reporting Fingerprint Evidence

Joseph B. Kadane and Jonathan J. Koehler

Everyone knows that fingerprint evidence can be extremely incriminating. What is less clear is whether the way that a fingerprint examiner describes that evidence influences the weight lay jurors assign to it. This essay describes an experiment testing how lay people respond to different presentations of fingerprint evidence in a hypothetical criminal case. We find that people attach more weight to the evidence when the fingerprint examiner indicates that he believes or knows that the defendant is the source of the print. When the examiner offers a weaker, but more scientifically justifiable, conclusion, the evidence is given less weight. However, people do not value the evidence any more or less when the examiner uses very strong language to indicate that the defendant is the source of the print versus weaker source identification language. We also find that cross-examination designed to highlight weaknesses in the fingerprint evidence has no impact regardless of which type of conclusion the examiner offers. We conclude by considering implications for ongoing reform efforts.

JOSEPH B. KADANE, a Fellow of the American Academy since 2010, is the Leonard J. Savage University Professor of Statistics and Social Sciences, Emeritus, at Carnegie Mellon University. His most recent book is Pragmatics of Uncertainty (2017).

JONATHAN J. KOEHLER is the Beatrice Kuhn Professor of Law at the Northwestern University Pritzker School of Law. He conducts research related to decision-making in the courtroom. His work has recently been published in such journals as Journal of Criminal Law and Criminology, Jurimetrics Journal, and Psychology, Public Policy, and Law.

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