NCJ Number
218834
Journal
Forensic Science Communications Volume: 1 Issue: 3 Dated: October 1999 Pages: 1-10
Date Published
October 1999
Length
10 pages
Annotation
This paper argues that the statistical model used in forensic DNA analysis is not appropriate for establishing the evidentiary value of trace evidence.
Abstract
The public and the courts expect forensic scientists, including trace evidence examiners, to use mathematics and statistics to show the overwhelming statistical likelihood that a particular individual was at a crime scene and/or had contact with a crime victim. This expectation carries pitfalls that could adversely influence the accuracy of evidentiary reports presented in court. The data upon which trace evidence statistics might be based differ radically from those used in DNA statistical calculations. If statistics are applied to show the distinctiveness of trace evidence and its relevance to issues to be decided in a criminal case, then they must be applied in a way that is appropriate to the discipline, unbiased in interpretation, and understandable to the trier of fact. Any statistical interpretation of a trace evidence finding must be based on a thorough knowledge of the population under study, necessarily through sampling, so as to determine the statistical basis for concluding that the trace evidence is unique in the larger population of similar materials, whether it is fiber, hair, glass, or other material whose properties can be measured. Since trace analysts currently lack the statistical tools of DNA analysts, they must show the significance of their findings with the only tool currently available to them, i.e., jury education. Properly done, jury education can instruct laypersons in the principles, practices, and underlying logic of the examinations performed and how they show that a particular piece of evidence examined is highly likely to connect a defendant to a crime scene or a crime victim. 32 references