National forensic science organization approves standards for interpreting DNA mixtures.
by the National Institute of Standards and Technology, U.S. Department of Commerce
The Organization of Scientific Area Committees (OSAC) for Forensic Science has placed two new standards covering the interpretation of DNA evidence on its registry of approved standards. This stamp of approval from OSAC, which is administered by the National Institute of Standards and Technology (NIST), indicates that these standards are technically sound and will help forensic laboratories improve their processes and methods.
OSAC is a professional organization whose 550-plus members have expertise in 25 forensic disciplines as well as scientific research, measurement science, statistics, law and policy. OSAC works to strengthen the practice of forensic science by facilitating the development and promoting the use of high-quality, science-based standards.
This milestone is the culmination of an effort that began in 2015. The two new standards were initially drafted by OSAC, then further developed and published by the Academy Standards Board (ASB) of the American Academy of Forensic Sciences, and finally reviewed by OSAC for placement on the registry. The new standards are:
- ANSI/ASB Standard 020, Standard for Validation Studies of DNA Mixtures, and Development and Verification of a Laboratory’s Mixture Interpretation Protocol.
- ANSI/ASB Standard 040, Standard for Forensic DNA Interpretation and Comparison Protocols.
Before laboratories can use a method to analyze crime scene evidence, they must perform validation studies and use the results of those studies to develop a protocol. These new standards include detailed requirements for conducting validation studies, developing protocols from them and verifying that those protocols work correctly.
In addition, the new standards are the first to focus on DNA mixtures, which occur when evidence contains DNA from multiple individuals. DNA mixtures can be more difficult to interpret than evidence that contains DNA from only one individual. Past studies have shown that different labs, or different analysts within a lab, sometimes produce different conclusions when evaluating the same DNA mixture. The new standards are aimed in part at helping labs achieve consistent and reproducible conclusions.
“Every forensic laboratory wants to put out the highest-quality data possible and the most accurate and reliable information and results,” said Robyn Ragsdale, a senior crime laboratory analyst at the Florida Department of Law Enforcement and chair of OSAC’s Biology/DNA Committee. “These standards will help them do that.”
Two aspects of the new standards in particular will help with this. First, the verification step must demonstrate that a laboratory’s protocols produce consistent and reliable conclusions with DNA samples different from the ones used in the initial validation studies. Second, the new standards require that labs not interpret DNA mixtures that go beyond what they have validated and verified. For example, if a lab has tested its protocol for up to three-person DNA mixtures, it should not interpret casework that contains DNA from four or more people.
These new standards complement the FBI’s DNA Quality Assurance Standards. Those standards mainly apply to laboratories that upload data to the FBI’s national DNA database, and they do not address how to develop and verify protocols for interpreting DNA mixtures.
The new standards also build upon guidelines published by the Scientific Working Group on DNA Analysis Methods, or SWGDAM. Guidelines are looser than standards in that they suggest best practices that laboratories should follow, while standards list requirements that labs must follow to be considered in compliance by an accrediting body.
Compliance with these new standards, as with almost all forensic science standards in the United States, is voluntary. However, some labs are already meeting or close to meeting these new standards. In addition, by adopting these standards, forensic labs can improve their processes and demonstrate their commitment to quality.
Additional standards are in the pipeline. For instance, the ASB is finalizing standards, also initially drafted by OSAC, for validating the probabilistic genotyping software that many laboratories use for interpreting DNA mixtures. The American National Standards Institute (ANSI) accredited standards development process at ASB together with the drafting and approval processes at OSAC involve multiple layers of technical review and ensure that standards are developed via a consensus process that invites input from all stakeholders prior to placement on the OSAC registry.
For more information on OSAC’s role in the standards development process, visit the OSAC website.
This article was originally published May 12, 2020, by the National Institute of Standards and Technology on NIST.gov; reprinted with permission.
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