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Revisiting the STRmix™ likelihood ratio probability interval coverage considering multiple factors

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posted on 22.04.2021, 04:07 by Jo-Anne Bright, Shan-I Lee, John Buckleton, Duncan Taylor

In previously reported work a method for applying a lower bound to the variation induced by the Monte Carlo effect was trialled. This is implemented in the widely used probabilistic genotyping system, STRmix™. The approach did not give the desired 99% coverage.

However, the method for assigning the lower bound to the MCMC variability is only one of a number of layers of conservativism applied in a typical application. We tested all but one of these sources of variability collectively and term the result the near global coverage. The near global coverage for all tested samples was greater than 99.5% for inclusionary average LRs of known donors. This suggests that when included in the probability interval method the other layers of conservativism are more than adequate to compensate for the intermittent underperformance of the MCMC variability component. Running for extended MCMC accepts was also shown to result in improved precision.

Funding

US National Institute of Justice - Grant No. 2020-DQ-BX-0022

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