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Taming Uncertainty in Forensic DNA Evidence

M.W. Perlin, "Taming uncertainty in forensic DNA evidence", European Network of Forensic Science Institutes (ENFSI) DNA Working Group meeting, Brussels, Belgium, 8-April-2011.


PowerPoint presentation with live audio recording of the European Network of Forensic Science Institutes 2011 talk.

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People and the courts may desire certainty, but all scientific data are inherently uncertain, including DNA evidence. Probability is used in science to describe uncertainty. Since forensic DNA is an information science, probabilistic computing can help objectively preserve maximal identification information. DNA information is simply a change in match probability based on the evidence.

We first introduce the key ideas of genotype (actual, data, inferred) and match (likelihood ratio) using simple genetic inheritance. We then apply these concepts to phenotype STR evidence data, comparing quantitative computer mixture interpretation with manual threshold methods. We next examine several cases to see how probabilistic computer interpretation of forensic DNA evidence can tame uncertainty in ways that human review cannot. We take a look at validation studies that establish that computer DNA interpretation is more powerful than human review. We conclude by considering the benefits to public safety of using scientific computing that preserves DNA evidence information.