We present a method for measuring the efficacy of eyewitness identification procedures by applying fundamental principles of information theory. The resulting measure evaluates the Expected Information Gain (EIG) for an identification attempt, a single value that summarizes an identification procedure’s overall potential for reducing uncertainty about guilt or innocence across all possible witness responses. In a series of theoretical demonstrations, we show that EIG often disagrees with existing measures (e.g., diagnosticity ratios or area under the ROC) about the relative effectiveness of different identification procedures. Each demonstration is designed to highlight “blind spots” of the existing measures as a contrast to EIG, which considers every factor relevant to a procedure’s potential for decreasing uncertainty about guilt or innocence. Collectively, these demonstrations show that EIG has substantial potential to inspire new discoveries in eyewitness research. For research designed to identify procedures that will be most effective in criminal investigations, EIG supersedes all other measures, on both theoretical and practical grounds.
A complete method for assessing the effectiveness of eyewitness identification procedures: Expected information gain.
