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Forensic Sci Int. 2017 Mar;272:e7-e9. doi: 10.1016/j.forsciint.2016.10.018. Epub 2016 Oct 26.

A comment on the PCAST report: Skip the "match"/"non-match" stage.

Author information

1
Independent Forensic Consultant, Vancouver, British Columbia, Canada; Adjunct Professor, Department of Linguistics, University of Alberta, Edmonton, Alberta, Canada; Simons Foundation Visiting Fellow, Isaac Newton Institute for Mathematical Sciences, Cambridge, England, United Kingdom. Electronic address: geoff-morrison@forensic-evaluation.net.
2
Distinguished Professor and Weiss Family Scholar, Penn State Law, Pennsylvania State University, University Park, PA, United States; Regents' Professor Emeritus, Arizona State University College of Law and Department of Life Sciences, Tempe, AZ, United States.
3
Professor of Statistical Genetics, Centre for Systems Genomics, School of Biomedical Sciences, and School of Mathematics & Statistics, University of Melbourne, Melbourne, Victoria, Australia.
4
Principal Scientist of Forensic Statistics, Forensic Science South Australia, Adelaide, South Australia, Australia; Associate Professor of Biology, School of Biological Sciences, Flinders University, Adelaide, South Australia, Australia.
5
Emeritus Professor of Statistics, Department of Pure Mathematics and Mathematical Statistics, University of Cambridge, Cambridge, England, United Kingdom.
6
Professor of Forensic Statistics, School of Mathematics, University of Edinburgh, Edinburgh, Scotland, United Kingdom.
7
Forensic Statistician, Statistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD, United States.
8
Associate Professor, Institute of Forensic Research, Krakow, Poland; Senior Lecturer, Chemometric Research Group, Institute of Chemistry, University of Silesia in Katowice, Poland.
9
Barrister, Wellington, New Zealand.
10
Director General, Forensic Science Ireland, Dublin, Ireland.
11
Independent Consultant, DNA Principal Forensics Ltd., Reading, England, United Kingdom.
12
Professor of Computer Science and Statistics, Risk Assessment and Decision Analysis Research Group, Department of Computer Science, Queen Mary, University of London, London, England, United Kingdom.
13
ARC DECRA Fellow & Senior Lecturer, School of Psychology, University of New South Wales, Sydney, New South Wales, Australia.
14
Senior Analyst, Innovative Decisions, Inc., Vienna, VA, United States.
15
Professor of Mathematical Probability, Department of Mathematics, Leiden University, Leiden, The Netherlands.
16
Director and Consultant Scientist, The Forensic Institute, Glasgow, Scotland, United Kingdom.
17
PhD Candidate (ABD), Department of Mathematics, University of Amsterdam, Amsterdam, The Netherlands.
18
Senior Forensic Document Examiner, Forensic Document Examination Section, Science and Engineering Directorate, Canada Border Services Agency, Ottawa, Ontario, Canada.
19
Forensic Statistician, Institute of Medical Informatics and Statistics, Kiel University, Kiel, Germany.

Abstract

This letter comments on the report "Forensic science in criminal courts: Ensuring scientific validity of feature-comparison methods" recently released by the President's Council of Advisors on Science and Technology (PCAST). The report advocates a procedure for evaluation of forensic evidence that is a two-stage procedure in which the first stage is "match"/"non-match" and the second stage is empirical assessment of sensitivity (correct acceptance) and false alarm (false acceptance) rates. Almost always, quantitative data from feature-comparison methods are continuously-valued and have within-source variability. We explain why a two-stage procedure is not appropriate for this type of data, and recommend use of statistical procedures which are appropriate.

KEYWORDS:

False alarm; Forensic statistics; Likelihood ratio; Match/non-match; PCAST report; Sensitivity

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