NIST Scientific Foundation Review on DNA Mixture Interpretation

In recent years, several scientific advisory bodies have expressed the need for a review of the scientific bases of forensic methods and identified NIST as an appropriate agency for conducting them. A scientific foundation review, also referred to as a technical merit evaluation, is a study that documents and assesses the foundations of a scientific discipline, that is, the trusted and established knowledge that supports and underpins the discipline’s methods. Congress has appropriated funds for NIST to conduct scientific foundation reviews in forensic science. These reviews seek to answer the question: “What established scientific laws and principles as well as empirical data exist to support the methods that forensic science practitioners use to analyze evidence?” Background information on NIST scientific foundation reviews is available in NISTIR 8225 at https://doi.org/10.6028/NIST.IR.8225.

DNA mixture interpretation was selected as the initial NIST scientific foundation review given the existence of abundant literature and a need expressed by members of the community. Multiple interlaboratory studies conducted by NIST and others have noted variability among accredited laboratories using validated approaches on the same DNA mixture data. The NIST team conducted this review with input from a Resource Group composed of 13 experienced practitioners and researchers.

After several years of study, a 250-page draft report, DNA Mixture Interpretation: A NIST Scientific Foundation Review, was released for public comment in early June 2021 (see https://doi.org/10.6028/NIST.IR.8351-draft). In six chapters, two appendices, and 528 references, this report examines the reliability and relevance of DNA mixture interpretation. A total of 25 key takeaways and 8 future considerations are provided along with 16 important principles underpinning DNA mixture interpretation. The likelihood ratio framework and probabilistic genotyping software are discussed along with the potential of new technologies to assist mixture interpretation. The report describes how the field has progressed over the past 35 years and strategies to strengthen it going forward. This presentation will discuss the process used to conduct this study, review findings reported, and describe feedback received during a 60-day public comment period.