“In 1993, in Daubert v. Merrell Dow Pharmaceuticals, Inc., the Supreme Court ruled that, under Rule 702 of the Federal Rules of Evidence (which covers both civil trials and criminal prosecutions in the federal courts), a ‘trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.’ The Court indicated that the subject of an expert’s testimony should be scientific knowledge, so that ‘evidentiary reliability will be based upon scientific validity.’ The Court also emphasized that, in considering the admissibility of evidence, a trial judge should focus ‘solely’ on the expert’s ‘principles and methodology,’ and ‘not on the conclusions that they generate.’ In sum, Daubert’s requirement that an expert’s testimony pertain to ‘scientific knowledge’ established a standard of ‘evidentiary reliability.’” – Committee on Identifying the Needs of the Forensic Sciences Community, National Research Council, Strengthening Forensic Science in the United States: A Path Forward