Presenting evidence in court
Presenting evidence in court
Presenting evidence in court
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1) Is the <strong>evidence</strong> based on a testable theory or technique;<br />
2) has the theory or technique been peer reviewed;<br />
3) <strong>in</strong> the case of a particular technique, does it have a known error rate and standards controll<strong>in</strong>g<br />
the techniques operation;<br />
4) is the underly<strong>in</strong>g science generally accepted<br />
As a general guide these rules make a lot of sense, stress<strong>in</strong>g scientific validity and the<br />
competence of the expert witness, but without requir<strong>in</strong>g consensus <strong>in</strong> the scientific community.<br />
The problematic part is, however, who is to be the judge if the <strong>evidence</strong> complies with these<br />
rules. In the US where Daubert has now been applied for some years the f<strong>in</strong>al word concern<strong>in</strong>g<br />
admissibility seems to have shifted from the scientific community to the trial judge who <strong>in</strong> most<br />
cases is likely to possess little or no competence to evaluate scientific validity and reliability. As<br />
may be expected this has not been without problems as I will expla<strong>in</strong>.<br />
F<strong>in</strong>ally, I will say a few words about <strong>in</strong>dividualization. The problem of <strong>in</strong>dividualization has a<br />
long history. One formulation of what it means for entities to be identical goes by the name of<br />
The Identity of Indiscernibles often referred to as Leibniz's law. Leibniz first formulated the<br />
pr<strong>in</strong>ciple <strong>in</strong> his Discourse on Metaphysics (1686): "it is not true that two substances may be<br />
exactly alike and differ only numerically". In logical terms the law is often re-formulated as: if,<br />
for every property F, object x has F if and only if object y has F, then x is identical to y. This is<br />
also by and large the way we th<strong>in</strong>k about identity <strong>in</strong> forensic speaker identification although we<br />
never come even close to the "for every property" requirement <strong>in</strong> any analysis. Two questions<br />
arise when we th<strong>in</strong>g about this law: 1) Is it true even <strong>in</strong> pr<strong>in</strong>ciple and 2) If it were can we even<br />
approach fulfilment of the requirements by any practically applicable methods <strong>in</strong> forensic<br />
science. Some scientist have argued that the pr<strong>in</strong>ciple is simply false, at least for some areas of<br />
Quantum Physics (Cortes, 1976). Others (e.g. Saks & Koehler, 2008) have attacked the pr<strong>in</strong>ciple<br />
on more practical grounds. Based on these and other studies, I will argue that we should abandon<br />
the concept of identity altogether <strong>in</strong> the forensic context.<br />
References<br />
Cortes, A. (1976). Leibniz's pr<strong>in</strong>ciple of the identity of <strong>in</strong>discernibles: A false pr<strong>in</strong>ciple. Philosophy of<br />
Science, 43(4): 491–505.<br />
Donnelly, P. (2005). Appeal<strong>in</strong>g statistics. Significance, 2(1), 46–48.<br />
National Research Council. (2009). Strengthen<strong>in</strong>g Forensic Science <strong>in</strong> the United States: A Path Forward.<br />
Wash<strong>in</strong>gton D.C.: The National Academies Press.<br />
Law Commission. (2011). Expert Evidence <strong>in</strong> Crim<strong>in</strong>al Proceed<strong>in</strong>gs <strong>in</strong> England and Wales. (LAW COM No<br />
325)<br />
Leibniz, G. W. (1686). Discourse on Metaphysics. (on-l<strong>in</strong>e translation by G. R. Montgomery.<br />
http://www.anselm.edu/homepage/dbanach/Leibniz-Discourse.htm)<br />
Saks, M. J. and J. J. Koehler (2008). The <strong>in</strong>dividualization fallacy <strong>in</strong> forensic science <strong>evidence</strong>. Vanderbilt<br />
Law Review, 61(1): 199–219.