Part I documents how courts have failed to faithfully apply Daubert’s criteria for scientific validity to this type of evidence. It describes how ambiguities and flaws in the terminology adopted in Daubert combinedwith the opaqueness of forensic-science publications and standards have been exploited to shield some test methods from critical judicial analysis. Simply desisting from these avoidance strategies would be an improvement. Part II notes how part of the U.S. Supreme Court’s opinion in Kumho Tire Co. v. Carmichael has enabled courts to lower the bar for what is presented as scientific evidence by mistakenly maintaining that there is no difference between that evidence and other expert testimony that need not be scientifically validated. It suggests that a version of Rule 702 that explicitly insists on more rigorous validation of evidence that is promoted or understood as being “scientific” would be workable and more clearly compatible with the rule’s common law roots. Part III sketches various meanings of the terms “reliability” and “validity” in science and statistics, on the one hand, and in the rules and opinions on the admissibility of expert evidence, on the other. It discusses the two-part definition of “validity” in the PCAST report and the proposed criteria for demonstrating scientific validity of subjective pattern-matching testimony. It contends that if “validity” means that a procedure (even a highly subjective one) for making measurements and drawing inferences is fit for its intended use, then whether test results that have higher error rates than the ones selected in the report might nevertheless assist fact finders who are also appropriately informed of the evidence’s probative value must be evaluated. Finally, Part IV articulates two distinct approaches to informing judges or jurors of the import of similarities in features: the traditional one in which examiners opine on the truth and falsity of source hypotheses and a more finely grained one in which criminalists report only on the strength of the evidence. It suggests that the rules for admitting scientific evidence need to be flexible enough to accommodate the latter, likelihood-based testimony when it has a satisfactory empirically established basis.


Law; Criminal Law; Evidence; Courts; Judges