A comment on the PCAST report: Skip the "match"/"non-match" stage.
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.
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.
Geoffrey Stewart
GS
Morrison
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.
David H
DH
Kaye
Professor of Statistical Genetics, Centre for Systems Genomics, School of Biomedical Sciences, and School of Mathematics & Statistics, University of Melbourne, Melbourne, Victoria, Australia.
David J
DJ
Balding
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.
Duncan
D
Taylor
Emeritus Professor of Statistics, Department of Pure Mathematics and Mathematical Statistics, University of Cambridge, Cambridge, England, United Kingdom.
Philip
P
Dawid
Professor of Forensic Statistics, School of Mathematics, University of Edinburgh, Edinburgh, Scotland, United Kingdom.
Colin G G
CGG
Aitken
Forensic Statistician, Statistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD, United States.
Simone
S
Gittelson
Associate Professor, Institute of Forensic Research, Krakow, Poland; Senior Lecturer, Chemometric Research Group, Institute of Chemistry, University of Silesia in Katowice, Poland.
Grzegorz
G
Zadora
Barrister, Wellington, New Zealand.
Bernard
B
Robertson
Director General, Forensic Science Ireland, Dublin, Ireland.
Sheila
S
Willis
Independent Consultant, DNA Principal Forensics Ltd., Reading, England, United Kingdom.
Susan
S
Pope
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.
Martin
M
Neil
ARC DECRA Fellow & Senior Lecturer, School of Psychology, University of New South Wales, Sydney, New South Wales, Australia.
Kristy A
KA
Martire
Senior Analyst, Innovative Decisions, Inc., Vienna, VA, United States.
Amanda
A
Hepler
Professor of Mathematical Probability, Department of Mathematics, Leiden University, Leiden, The Netherlands.
Richard D
RD
Gill
Director and Consultant Scientist, The Forensic Institute, Glasgow, Scotland, United Kingdom.
Allan
A
Jamieson
PhD Candidate (ABD), Department of Mathematics, University of Amsterdam, Amsterdam, The Netherlands.
Jacob
J
de Zoete
Senior Forensic Document Examiner, Forensic Document Examination Section, Science and Engineering Directorate, Canada Border Services Agency, Ottawa, Ontario, Canada.
R Brent
RB
Ostrum
Forensic Statistician, Institute of Medical Informatics and Statistics, Kiel University, Kiel, Germany.
Amke
A
Caliebe
False alarm; Forensic statistics; Likelihood ratio; Match/non-match; PCAST report; Sensitivity