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DNA Transfer - an ongoing conundrum - and the problem of considering simple experience as expertise

Research into the phenomenon of DNA transfer continues (see our previous comments).  It appears that the more we know, the more we appreciate that this is perhaps a more complicated topic than first appeared.  While there are some who believe that the DNA profile can tell us how the DNA was deposited, we do not believe that there is enough research to support such opinions.

Breathnach et al recently published the results of their work looking at specific scenarios of DNA transfer[i].  They claimed that this work, combined with the experience of the expert, now enabled the assessment of not only the possibility of DNA transfer but also the  probability of transfer via wearing, touching and indirect transfer to worn items of clothing.  Having previously published an extensive review of the research in this area[ii], we found this conclusion surprising.  We prepared and published a response to Breathnach et al, basically setting out our view that such broad assertions could not be supported by the limited evidence[iii].  As is customary and correct, Breathnach et al were invited to respond to our criticism, which they duly did[iv].

While not disagreeing that the literature was insufficient to support probabilistic opinions, Breathnach et al continued to maintain that,

“the scientist has knowledge about the transfer and persistence of DNA which facilitates him or her in assessing the likelihood of observing a particular DNA result given competing propositions as posed by the prosecution and defence. We believe, it is the scientist’s responsibility to share this information with the lawyers, jury and police so their decisions are better informed. …

The main difference between our position and that of Jamieson and Bader is that we consider it useful to assist the triers of fact by providing guidance on the interpretation”

This argument has been made recently in a response to our review of the research[v].  Our response was published and included,

“We consider that in the current state of research in DNA transfer, the safest and scientifically justifiable approach is to advise the court that it is not possible to provide a scientifically reliable opinion on the route of transfer given the paucity of published data and the number of unknown factors involved. We wish that it was not so, but wishful thinking, or a desire to be ‘helpful’ is not enough. However, if unpublished data are to be relied upon, then these should be made available to the defence to allow a proper scientific scrutiny of the basis of any evaluative opinion offered. Likewise, if casework experience is proffered as the source of an evaluative opinion, then it should be clearly explained how such experience has informed the opinion; quoting ‘x years of casework experience’ is simply not sufficient.”[vi]

We, and others, have already published views on the inadequacy of ‘experience’ in this area[vii], [viii] , [ix].  Most recently, our view has been endorsed by the President’s Council of Advisors on Science and Technology (PCAST), an advisory group of leading scientists and engineers, appointed by the President of the United States to provide scientific advice.  In September 2016, PCAST released a critique of several methods used in ‘forensic science’[x].  They were scathing about the use of experience as justification for a scientific opinion;

“Similarly, an expert’s expression of confidence based on personal professional experience or expressions of consensus among practitioners about the accuracy of their field is no substitute for error rates estimated from relevant studies. For forensic feature-comparison methods, establishing foundational validity based on empirical evidence is thus a sine qua non. Nothing can substitute for it.” [our emphasis]

An article authored by us in Barrister Magazine discusses the PCAST report with a special emphasis on probabilistic genotyping systems. 

We continue to maintain these views on DNA transfer and so-called expert opinion based on experience.  We have presented them in court, and prior to court, in many criminal cases.  We will continue to do so until and unless the evidence suggests otherwise.

October 2016



[i] Breathnach, M. et al., Forensic Science International: Genetics 20 (2016) 53–60)

[ii] Meakin, G., Jamieson, A., Forensic Science International: Genetics 7 (2013) 434–443

[iii] Jamieson & Bader, FSI Genetics, ??? (2016)

[iv] Breathnach et al., Forensic Science International: Genetics xxx (2016) xxx 10.1016/j.fsigen.2016.10.001

[v] Casey et al., Forensic Science International: Genetics 21 (2016) 117–118

[vi] Meakin & Jamieson, FSI:Genetics (2016) http://dx.doi.org/10.1016/j.fsigen.2016.02.010

[vii] N.N. Daéid, Sci. Justice 50 (2010) 111–112

[viii] P. Gill, Misleading DNA Evidence: Reasons for Miscarriages of Justice, Academic Press, 2014

[x]  President’s Council of Advisors on Science and Technology.  Report to the President Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods. September 2016

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