Online Workshop Series: Probabilistic Genotyping Of Evidentiary DNA Typing Results

The Federal Bureau of Investigation Laboratory has partnered with the National Institute of Justice’s Forensic Technology Center of Excellence to create a series of online workshops aimed at increasing knowledge, understanding, and the reliable application of probabilistic genotyping to evidentiary DNA typing results. Targeting DNA scientists in the forensic laboratory and legal professionals hearing DNA evidence in court, lectures begin with fundamental information and increase in complexity to address a variety of topics relevant to the development and use of probabilistic genotyping in criminal investigations, from the laboratory to the courtroom.

We begin by covering fundamental aspects of interpreting DNA results, as well as factors that impact DNA typing results, such as the transfer and persistence of DNA on evidence and stochastic effects. Particular consideration is given to the interpretation of low-template evidence, as exemplified in the Amanda Knox case.

The tenets of probabilistic genotyping are introduced, including statistical aspects and mechanisms of computer-assisted analysis. Lecturers walk you through the reasoning behind setting propositions that reflect case scenarios and whether, say, a suspect left the DNA on the evidence. Likelihood ratios are calculated and discussed. Three fully continuous software systems will be presented by the respective developers, with the goal of enabling participants in the session to understand the features, basic functioning, capabilities, and limitations of the software programs.

Lecturers will also share their experience in validating probabilistic genotyping systems, noting particular studies that were critical to the development of standard operating procedures within their laboratories. They will discuss research and data generated in the course of validation studies that were used to assess uncertainty and limitations of the software.

Historically, the predominant means of assigning statistical weight to many DNA mixtures in the U.S. has been the combined probability of inclusion, or CPI. Accordingly, many forensic DNA analysts, as well as attorneys and judges, are well-versed in the CPI as a match probability. In this series, we devote two sessions to helping DNA analysts and legal professionals to understand degrees of statistical weight and properly communicate likelihood ratios and their meaning. The SWGDAM recommendations for reporting likelihood ratios will be discussed, along with an explanation of the empirical basis for its verbal scale that may be used in reports and testimony along with the likelihood ratio. Participants’ ears will be tuned to lines of questioning that could lead to a fallacious statement about the statistic. The U.S. Department of Justice Uniform Language for Testimony and Reporting will be imparted.

The status of probabilistic genotyping in U.S. courts will be detailed, including its use in criminal proceedings and admissibility hearing outcomes. Representatives of STRmix™ and TrueAllele® will share examples of successful case outcomes and issues addressed in court.

The series is comprised of the modules listed below. You will have the opportunity to pose questions to the lecturers during each session. A tentative overflow session is designated as a conclusion to the series.