Interpretation

Forensic scientists, examining an object, pattern, or impression, observe and measure physical or chemical features. They then interpret these measurements to assist investigators, lawyers, and judges or juries. Ultimately, the task of the forensic scientist is not to decide what legal investigators, judges, or jurors should believe, but to supply accurate and useful information to these decision makers. This article therefore concerns the task of translating laboratory measurements into statements that will assist legal fact finders in evaluating hypotheses about the events that are relevant in legal disputes. It introduces the likelihood ratio as a measure of the probative value of evidence in its own right and outlines the Bayesian framework for moving from data to beliefs in hypotheses. It examines common interpretive practices from this perspective and in light of the needs of the legal system.