Communicating Toxic Risk to Judges and Juries. Wayne Roth-Nelson; Roth-Nelson Science, 8663 Hollyhock Lane, Lafayette, CO 80026
Risk science in the courtroom can become adversarial and confuse both judge and jury. A jury may treat an expert’s risk numbers as the unambiguous truth if the cross-examination falls to reveal how the scientist must choose from a wide range of possible assumptions and models. In real-world risk science, the numbers are clouded by uncertainties. It is the business of the courts, using written and oral expert testimony, to bring these uncertainties into evidence, however frustrating to judge and jury. Jurors may have difficulty understanding that probabilistic evidence of health risk only establishes a statistical association as circumstantial proof of disease causation in a population. Such evidence provides only a partial inference of individual causation. Some legal scholars argue that the true standard of proof invoked in the courts in intuitive and qualitative. In meeting the evidentiary standard, judges and juries may be misled by numerical expressions of probability. Jurors may dismiss the probabilistic evidence when presented with several conflicting views on both sides of the case. Juries may tend to treat scientific data as infallible or ignore the data in favor of the expert’s generalized opinion testimony. In many complex cases, any inadequacies in the jury deliberations are masked by the fact that a verdict for either party appears to be reasonable. Some interviews of judges, lawyers, expert witnesses and jurors have revealed that statistics are less persuasive than people, and that anecdotal evidence is more persuasive that expert data. An expression of ignorance or uncertainty, even if accurate, is often less persuasive that a plausible theory, even a false one. While there are legal definitions of proper and improper evidence, jurors view evidence as a form of story or narrative. The clear and well-told story is considered effective evidence, whereas the unclear, nonsensical story or not. One way to reduce "junk science" verdicts is to reduce the scope of scientific questions that juries must resolve for themselves, particularly by pretrial screening of probabilistic or risk evidence.