A comment on the PCAST report: Skip the "match"/"non-match" stage.

This letter comments on the report "Forensic science in criminal courts: Ensuring scientific validity of feature-comparison methods" recently released by the President's Council of Advisors on Science and Technology (PCAST). The report advocates a procedure for evaluation of forensic evidence that is a two-stage procedure in which the first stage is "match"/"non-match" and the second stage is empirical assessment of sensitivity (correct acceptance) and false alarm (false acceptance) rates. Almost always, quantitative data from feature-comparison methods are continuously-valued and have within-source variability. We explain why a two-stage procedure is not appropriate for this type of data, and recommend use of statistical procedures which are appropriate.

The design of "the first experimental study exploring DNA interpretation".

This letter explains why a recent study purporting to show that exposure to domain-irrelevant information caused DNA analysts to misinterpret a complex mixture does not warrant this conclusion on the basis of the data from the study.

Science in the jury box: jurors' comprehension of mitochondrial DNA evidence.

Questions about how jurors understand and apply scientific evidence were addressed in a mock jury study in which 480 jury pool members watched a videotaped mock trial that included expert testimony about mitochondrial DNA (mtDNA) evidence purportedly linking a defendant to a crime. Collectively, jurors showed moderately good comprehension of the mtDNA evidence, although some made definitional and inferential errors. Comprehension was better among jurors with higher educational attainment and more mathematics and science courses. Lower comprehension was associated with jurors' reservations about science and concerns about the contamination of mtDNA evidence. The results suggest that most jurors are capable of comprehending and employing scientific evidence presented during trial, although errors and doubts about the evidence should be anticipated.

The good, the bad, the ugly: the NAS report on strengthening forensic science in America.

In the long run, the NRC report can only have a salutary effect on forensic science. Although the report is not exhaustive in its review of the relevant literature and the law, and although broad constituencies may never embrace its most radical proposals, the report exposes the soft underbelly of a range of technologies, the organizational problems with the institutions that generate forensic science evidence, and the timidity of the courts in pushing for better science. Even if the full promise of the report is not realized, its publication ultimately should strengthen the good in a system of law and science that has its fair share of the good, the bad, and the ugly.