STRmix™ collaborative exercise on DNA mixture interpretation

Abstract

Highlights Inter-laboratory study with 174 participants using STRmix™  CE analysis settings resulted in larger differences in LR than PG software  Differences in log(LR) due to MCMC variation were less than one order of magnitude Abstract (max 400 words)An intra and inter-laboratory study using the probabilistic genotyping (PG) software STRmix™ is reported. Two complex mixtures from the PROVEDIt set, analysed on an Applied Biosystems™ 3500 Series Genetic Analyzer, were selected. 174 participants responded.LRs were assigned, the point estimates ranging from 2 × 10 4 to 8 × 10 6 . For Sample 2 (in the order of 2000 rfu for major contributors), LRs ranged from 2 × 10 28 to 2 × 10 29 . Where LRs were calculated, the differences between participants can be attributed to (from largest to smallest impact): varying number of contributors (NoC), the exclusion of some loci within the interpretation,  differences in local CE data analysis methods leading to variation in the peaks present and their heights in the input files used,  and run-to-run variation due to the random sampling inherent to all MCMC-based methods.This study demonstrates a high level of repeatability and reproducibility among the participants. For those results that differed from the mode, the differences in LR were almost always minor or conservative.

Perceptions and estimates of error rates in forensic science: A survey of forensic analysts

“…In other words, the same examiner, looking at the same pair of fingermarks, will reach a different conclusion 10% of the time [18]. A past study examining the reliability of DNA analyses showed some inconsistency in conclusions [19], and this has recently been replicated by a number of studies showing great variability in DNA results when analyzing the same sample (e.g., some included alleles that were absent, others neglected alleles that were present) further indicating that errors in DNA do exist [20][21][22]. Although DNA analysis is widely regarded as the prevailing standard of forensic science [3], "we do not know any more about human or laboratory error rates in DNA cases than we know about human or laboratory error rates in cases that employ other forensic science techniques" ( [23], p. 3).…”

(Draft) DNA Mixture Interpretation

“…In their article describing the PROVEDIt data set, the authors express their hope that "a large dataset would play a critical role in demonstrating the foundational validity and robustness of new or existing DNA identity testing technology" (Alfonse et al 2018). Samples from the PROVEDIt data set have been used in PGS comparisons (e.g., Riman et al 2019b) and interlaboratory studies (e.g., Bright et al 2019a). ______________________________________________________________________________________________________ This publication is available free of charge from: https://doi.org/10.6028/NIST.IR.8351-draft…”

“…As forensic laboratories share their validation summaries and data used for making decisions to enable future independent review of their work, the field has the opportunity to be strengthened. Tables with sample details and LR values have been made available as supplemental files in some publications (e.g., Bright et al 2019a, Rodriguez et al 2019.…”

Problematic reporting in DNA cases: the need for accredited formats and certified reporting competence

“…With the generalisation of probabilistic genotyping software, collaborative exercises have been initiated [6,7], guidelines and even standards have been generated (ISFG, For. Reg., SWGDAM).…”