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Archived Comments for: Lab Retriever: a software tool for calculating likelihood ratios incorporating a probability of drop-out for forensic DNA profiles

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  1. Clarification of some comments in Inman et al. 

    John Buckleton, ESR

    16 December 2015

    There is a worldwide interest in methods and software to perform probabilistic genotyping.  Trials comparing the performance of these software with present methods are useful to laboratories making decisions about changes to interpretation strategies. 

    The Inman et al. paper [1] has a considerable section discussing our own paper comparing Lab Retriever with CPI, RMP and STRmix [2].  As a bit of background Lab Retriever implements the mathematics in Balding and Buckleton (B&B) [3].   That mathematics descends from earlier work by Buckleton undertaken in 1999 and published in Gill et al [4].  One of the authors of this note is therefore, in part, the originator of the method encapsulated in Lab Retriever.  The idea behind the semi-continuous methods was Buckleton’s first effort at dealing with drop-out probabilistically.  It has been surpassed by continuous models.  Even the drop-out probability for homozygotes in B&B has been surpassed by the work of Tvedebrink et al. [5].

    Despite these comments we do not consider ourselves to be critics of Lab Retriever.  All implementations make compromises.  We actually consider change from CPI to almost any other option to add strength to interpretation.

    Inman et al. suggest errors exist in our treatment of stutters and of minor profiles in a major minor mixtures.  We have re-examined the work and cannot find any errors in our treatment.  We are happy to provide Inman et al. with the raw data.  Subsequent to the submission of this paper we learnt, from Carlos Baezer-Richer [6], of a work around used in LRmix for the minor profile in a major minor mixture.  We have tested this and it also works in Lab Retriever except that the answer should be divided by 2 [7].  We have passed this information to the Lab Retriever developers. 

    We would also like to confirm that our analytical threshold (AT) was empirically derived and complies with SWGDAM 2010 [8].  In comparative studies it is necessary to apply the same AT to all methods.

    The article by Inman et al. suggests that our comments are driven by bias. In the case of Buckleton he is commenting on his own work, albeit of up to 16 years ago.


    Bille TW,

    Weitz SM,

    Coble MD,

    Buckleton JS,

    Bright J-A



    [1] Inman K, Rudin N, Cheng K, Robinson C, Kirschner A, Inman-Semerau L, et al. Lab Retriever: a software tool for calculating likelihood ratios incorporating a probability of drop-out for forensic DNA profiles BMC Bioinformatics. 2015;16:298.

    [2] Bille TW, Weitz SM, Coble MD, Buckleton JS, Bright J-A. Comparison of the performance of different models for the interpretation of low level mixed DNA profiles. ELECTROPHORESIS. 2014;35:3125-33.

    [3] Balding DJ, Buckleton J. Interpreting low template DNA profiles. Forensic Science International: Genetics. 2009;4:1-10.

    [4] Gill P, Whitaker JP, Flaxman C, Brown N, Buckleton JS. An investigation of the rigor of interpretation rules for STR's derived from less that 100 pg of DNA. Forensic Science International. 2000;112:17-40.

    [5] Tvedebrink T, Eriksen PS, Mogensen HS, Morling N. Estimating the probability of allelic drop-out of STR alleles in forensic genetics. Forensic Science International: Genetics. 2009;3:222-6.

    [6] Bright J-A, Evett IW, Taylor D, Curran JM, Buckleton J. A series of recommended tests when validating probabilistic DNA profile interpretation software. Forensic Science International: Genetics. 2015;14:125-31.

    [7] Taylor D, Bright J-A, Buckleton J. The ‘factor of two’ issue in mixed DNA profiles. Journal of Theoretical Biology. 2014;363:300-6.

    [8] Scientific Working Group on DNA Analysis Methods (SWGDAM). SWGDAM Interpretation Guidelines for Autosomal STR Typing by Forensic DNA Testing Laboratories. 2010.

    Competing interests

    John Buckleton is the co-author of the theory underlining Lab Retreiver.