Thursday, June 15, 2017

Let's talk about forensic science: week one

Your friendly blog post writer was fortunate enough to attend the National Forensic College last week at Cardozo Law school in New York. The college provided a six day intense focus on forensic science issues ranging from DNA to digital evidence. So the Thursday spot on the blog will be used to share a few of the very helpful tips that were passed on during this program.

We start with a topic that has been mentioned before, but deserves greater discussion - the PCAST report. As we discussed back in October, the PCAST report was prepared by leading scientists and engineers for the purpose of answering questions created by the 2009 National Resource Counsel report on strengthening forensic science in the United States. As we know now, this administration is not interested in answering those questions or strengthening forensic science.



Everyone should at least read the executive summary of the report. It is 20 pages and does a great job summarizing their findings. For example do you have a case where a bitemark is used as evidence? PCAST is not impressed: "Bitemark analysis is a subjective method. Current protocols do not provide well-defined standards concerning the identification of features or the degree of similarity that must be identified to support a reliable conclusion that the mark could have or could not have been created by the dentition in question."

This week starts with an easy but important concept from those early pages - the difference between foundational validity and validity as applied. Foundational validity establishes that the scientific method used is repeatable, reproducible, and accurate. That means that a person performing the test can perform the test the same way multiple times and get the same result. It also means that a different person can do the same test the same way and get the same result. Finally, it means that result is accurate. If all three are met, then a certain method can, in principle, be reliable. This corresponds with the legal requirement in Rule 702(c) of using "reliable principles and methods."

Validity as applied means that the method has been reliably performed in practice. This means that a foundationally valid method can still be inadmissible if the person performing the test does not properly implement an otherwise reliable method. This corresponds with Rule 702(d) while requires an expert to "reliably apply the principles and methods to the facts of the case."

Keep these concepts in mind as we discuss some tips from specific areas of forensic science in the next few weeks.

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