Forensic scientists frequently offer opinions in complex or technical domains about which lay people have limited knowledge. The statistical evidence presented by forensic scientists may include uncertainty statements, information about error, base rates, random match probabilities, false-report probabilities, and likelihood ratios. Where once the opinions of forensic practitioners' were communicated in terms of unqualified categorical matches or “individualization,” now many forensic practitioners propose more complex formulations. Confronted with complexity, some forensic practitioners have attempted to translate statistical evidence, and impressions of the strength of evidence, into qualitative expressions (“verbal scales”). Ascertaining how well jurors understand statistical statements requires us to define and measure “understanding” in the context of a complex decision-making environment. Such understanding can be studied with indicia of consistency, sensitivity, coherence, ability, and orthodoxy (CASOC). This chapter describes the methodology of CASOC studies and reviews the findings on juror comprehension of statistical statements in relation to each of these indicia.