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In this publication we compile the STRmix™ internal validation material from 31 laboratories, which allows a novel look at data spanning laboratory technology and process. We report the analysis of 2825 mixtures compiled from the 31 laboratories (including multi laboratory systems) who are using STRmix™ in casework (28/31) or currently validating STRmix™ for future use in casework (3/31). Mixtures of three, four, five, and six contributors are specifically targeted in order to address the three key areas where PCAST felt additional validation would be merited:
(1) How well does the method perform as a function of the number of contributors to the mixture? How well does it perform when the number of contributors to the mixture is unknown?
(2) How does the method perform as a function of the number of alleles shared among individuals in the mixture? Relatedly, how does it perform when the mixtures include related individuals?
(3) How well does the method perform—and how does accuracy degrade—as a function of the absolute and relative amounts of DNA from the various contributors?
With over 10,000 Hp true tests and 28,250,000 Hd true tests we demonstrate the foundational validity of STRmix™ for complex, mixed DNA profiles to levels well beyond the complexity and contribution levels suggested by PCAST.