Finding the way forward for forensic science in the US:a commentary on the PCAST report

A recent report by the US President’s Council of Advisors on Science and Technology (PCAST) [1] has made a number of recommendations for the future development of forensic science. Whereas we all agree that there is much need for change, we find that the PCAST report recommendations are founded on serious misunderstandings. We explain the traditional forensic paradigms of match and identification and the more recent foundation of the logical approach to evidence evaluation. This forms the groundwork for exposing many sources of confusion in the PCAST report. We explain how the notion of treating the scientist as a black box and the assignment of evidential weight through error rates is overly restrictive and misconceived. Our own view sees inferential logic, the development of calibrated knowledge and understanding of scientists as the core of the advance of the profession

A comparison of stochastic variation in mixed and unmixed casework and synthetic samples

Understanding the behaviour of mixed DNA profiles is of paramount importance in forensic DNA analysis. Key parameters are those of heterozygote balance and mixture proportion and its variability. These parameters have been previously explored as a function of the average peak height of the active alleles in single source and mixed samples derived from pristine DNA. Here we report a comparison of this data with data obtained from casework samples. This allows an assessment of the difference in the distribution of heterozygote balance between mixed and single source stains and between casework mixtures and synthetic mixtures constructed from pristine DNA

DNA profiling and criminal justice a contribution to a changing debate

Forensic DNA profiling is now a routine feature of the criminal justice system in Australia. Its applications in this context continue to increase. Technological advancements and the use of DNA databases have facilitated the uptake of biological evidence into criminal investigations. The development of DNA methodology has progressed through discernable phases that have been paralleled by discussion amongst the legal community. The context of development and the associated debate has changed. lt now encompasses broader issues, concerned less specifically with the technology itself and more with the most appropriate means for its use. To contribute more purposefully to this debate and to achieve the most meaningful outcomes from the criminal justice system, we must first understand more holisticallv the role that DNA evidence plays and the impact that it is capable of. This paper reviews aspects of the forensic and legal contexts of the use of DNA technology in the Justice system. This is a prelude to future research and a justification for the need for such research

The factor of 10 in forensic DNA match probabilities

© 2017 An update was performed of the classic experiments that led to the view that profile probability assignments are usually within a factor of 10 of each other. The data used in this study consist of 15 Identifiler loci collected from a wide range of forensic populations. Following Budowle et al. [1], the terms cognate and non-cognate are used. The cognate database is the database from which the profiles are simulated. The profile probability assignment was usually larger in the cognate database. In 44%–65% of the cases, the profile probability for 15 loci in the non-cognate database was within a factor of 10 of the profile probability in the cognate database. This proportion was between 60% and 80% when the FBI and NIST data were used as the non-cognate databases. A second experiment compared the match probability assignment using a generalised database and recommendation 4.2 from NRC II (the 4.2 assignment) with a proxy for the matching proportion developed using subpopulation allele frequencies and the product rule. The findings support that the 4.2 assignment has a large conservative bias. These results are in agreement with previous research results