Communicating the Results of Forensic Science Examinations

Abstract

During the 20th century, forensic scientists traditionally relied on heuristic techniques to analyze and compare forensic science evidence that can help link a suspect or defendant to the location or victim of a crime. They commonly reported categorical opinions on the evidence in courts. Drawing on developments in forensic statistics and DNA evidence, legal and scientific scholars have pressed forensic scientists to measure the validity and reliability of their techniques and to evaluate and quantify the weight of the evidence in each case in a fair, balanced and transparent fashion. A successful transition from an opinion-based system to one in which measurements are more quantitative and opinions are supported by statistical analyses requires investigating the nature of forensic inference processes and the findings of cognitive psychology on how to best convey scientific information to decision makers.

This report on communicating the results of forensic science examinations was prepared for the Office of Law Enforcement Standards (OLES) of the National Institute of Standards (NIST) following the creation of an expert working group selected to provide expertise in forensic science, law, psychology, and statistics. It includes an overview of the nature of forensic inference (written by Graham Jackson); a survey of the current modes of presenting forensic identification findings (David Kaye); a review of jury studies and the psychology of efficient communication (Cedric Neumann and Valerie Reyna); conclusions and recommendations for improving communication (Cedric Neumann and Anjali Ranadive). Also included is a pilot study performed by Damon Bayer, Cedric Neumann, and Anjali Ranadive designed to compare the understanding and rational usage of forensic information by individuals confronted with likelihood ratios presented in different manners and to explore the challenge of measuring people’s understanding of that information.

Notes: This report is intended to reflect only the opinions of the authors. The working group as a whole was not asked to approve the contents, and it has not done so.

Keywords: forensic science, scientific evidence, identification, inference, interpretation, probative value, communicating probabilities, likelihood ratio, Bayes, fuzzy trace theory, cognitive heuristics