DNA mixture interpretation outside of the forensic laboratory? Apparently not yet.

The National Institute of Standards and Technology has published a draft report entitled DNA Mixture Interpretation: A Scientific Foundation Review.

As NIST explains:

This report, currently published in draft form, reviews the methods that forensic laboratories use to interpret evidence containing a mixture of DNA from two or more people.

From https://www.nist.gov/dna-mixture-interpretation-nist-scientific-foundation-review

The problem of mixtures is more pronounced in DNA analysis than in analysis of other biometrics. You aren’t going to encounter two overlapping irises or two overlapping faces in the real world. (Well, not normally.)

You can certainly encounter overlapping voices (in a recorded conversation) or overlapping fingerprints (when two or more people touched the same item).

But there are methods to separate one biometric sample from another.

It’s a little more complicated when you’re dealing with DNA.

Distinguishing one person’s DNA from another in these mixtures, estimating how many individuals contributed DNA, determining whether the DNA is even relevant or is from contamination, or whether there is a trace amount of suspect or victim DNA make DNA mixture interpretation inherently more challenging than examining single-source samples. These issues, if not properly considered and communicated, can lead to misunderstandings regarding the strength and relevance of the DNA evidence in a case.

From the Abstract in https://doi.org/10.6028/NIST.IR.8351-draft%C2%A0

As some of you know, I have experience with “rapid DNA” instruments that provide a mostly-automated way to analyze DNA samples. Because these instruments are mostly automated and designed for use by non-scientific personnel, they are not able to analyze all of the types of DNA that would be analyzed by a forensic laboratory.

Therefore, this draft document is silent on the topic of rapid DNA, despite the fact that co-author Peter Vallone has years of experience in rapid DNA.

I am not a scientist, but in my view the absence of any reference to rapid DNA strongly suggests that it’s premature at this time to apply these instruments to DNA mixtures, such as rape cases in which both the assailant’s and the victim’s DNA are present in a sample.

Granted, there may be rape cases in which the DNA of the assailant may be present with no mixture.

You have to be REALLY careful before claiming that rapid DNA instruments can be used to wipe out the backlog of rape test kits. However, rapid DNA can be used to clear less complicated DNA cases so that the laboratories can concentrate on the more complex cases.

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