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Summary of miscodes

Wednesday, 23 May 2018

Updated Tuesday, 29 May 2018

During the lifetime of the STRmix™ project we have detected eight coding faults that act on the reported LR.  In no case was an inclusion found to be changed to an exclusion or vice versa.

  1. Present in versions up to (but not including) V1.08.  It affected the LR in an exceptionally minor way and produced neither false inclusions nor exclusions.  It was detected by a third party laboratory repeating calculations by hand.  It did not result in the need to reissue any statements.  Statement-on-minor-miscoding-in-BN-formulae-STRmix-V1-08-with-additional-comments.pdf [PDF, 275 KB]
  2. Present in STRmix™ versions up to (but not including) version 2.0.6.  This was discovered after a case was brought to Forensic Science South Australia’s attention in December 2014 by Queensland Health.  This miscode was reported, with errors in the reporting, in the press.[1] The miscode affects the numerical value of the LR in rare instances and does not change an inclusion into an exclusion.  All potentially affected cases in Australia and New Zealand were examined and very few instances of a different LR occurred outside Queensland.  There are no known false inclusions as a result of the miscode.  To get an effect from this miscode a specific set of circumstances is needed which we believed quite unlikely to occur and which had not been specifically tested in developmental validation prior to this date.  Statement-relating-to-STRmix-miscodes-180316.pdf [PDF, 216 KB]
  3. Involved rare cases with multiple dropped alleles across all contributors within the one locus. This was found to be due to a change in STRmix™ that was introduced in the V2.3 series and has been present in all versions subsequent to this up to V2.3.09 and V2.4.04 (inclusive). The effect on likelihood ratios (LRs) is in a conservative direction and very minor.  Variation-in-STRmix-regarding-expected-heights-of-dropped-out-peaks-040716-ws.docx.pdf [PDF, 589 KB]
  4. Present in V1.0 to V2.4.05 for drop-in modelling and V2.4 to V2.4.05 for forward stutter modelling.  This affects only the database search LR (assuming the presence of forward stutter peaks and/or multiple drop-in alleles, and modelling of these artifacts was enabled) and to the Highest Posterior Density (HPD) calculations.  There was no detectable effect on the LR in a number of trials.  STRmix-v2-4-06-Description-of-changes-ws.docx.pdf [PDF, 846 KB]
  5. Present in all versions preceding V2.4.08 – three miscodes described below. Description-of-the-LR-changes-in-STRmix-v2-4-08-ws.pdf.pdf [PDF, 600 KB]

    5.1.    A change has been made to LR calculation (unrelated point estimate, stratified, unified and HPD) for mixed DNA profiles when there are multiple contributors considered under Hp who are unknown under Hd.  The contributors must have dropped alleles (either the same or different) at the same locus.  Changes were usually less than a factor of 10. 

    5.2.   A change has been made to the way drop-in alleles are assigned within the determination of the genotype array within pre burn-in.  This will affect all LR calculations including within the database search (standard and familial LRs), unrelated and related scenarios.  Changes in the LR were usually less than one order of magnitude. 

    5.3.   A minor anomaly in the familial search LR was identified.  The issue affected mixed and single source profiles with dropout where on some occasions an incorrect allele frequency was assigned to the alleles.  The comparison of LRs between versions indicates that this was mostly within one order of magnitude.

  6. A change was made to the way the seed was calculated affecting all versions preceding V2.3.07.  In previous versions the seed was randomised on startup by multiplying the day by hour by minute by second.  Between 0000hrs and 0100hrs the seed did not reset and the same seed was used for all calculations.  This only affected multiple interpretations that were started within this hour.  The seed is used within the random number generator within STRmix™.

 

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