But doesn’t that mean it is ‘more likely than not’?

When an examiner expresses an opinion along the lines of ‘the findings support one proposition over another proposition’, a question often follows. Specifically, does that opinion mean ‘it is more likely than not that the favored proposition actually happened’?1 The short answer is “no, it does not mean that.” At least, not necessarily.

In order to reach such a conclusion one must consider information that goes beyond the FDE evidence. As a rule, any opinion I provide will be constrained to the probability of the findings/observations in terms of one of at least two possible explanations.2 Ultimately, equating the two statements is inappropriate because they are not equivalent.

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Science vs Pseudoscience

Years ago, in 2013 to be precise, I was invited to speak at the ICA conference held in Montréal, Québec.  The conference had a special session on “distinguishing between science and pseudoscience in forensic acoustics”. Now, I am definitely not an expert in forensic acoustics.  In fact, I know almost nothing about the field other than what I’ve read from time to time. So I wasn’t there to tell the audience anything about forensic acoustics, per se.

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Book announcement: Forensic Document Examination in the 21st Century

FDE in the 21st CenturyI am very pleased to have been contributor to a new textbook, Forensic Document Examination in the 21st Century.  The text was edited by Jan Seaman Kelly and Miriam Angel and will be published by CRC Press.

My personal contribution is chapter 3 entitled “The Logical Approach to Evidence Evaluation”.   The complete list of contributors is impressive and includes Jan Seaman Kelly, Miriam Angel, Brett M.D. Bishop, Rigo Vargas, Mara L. Merlino, Samiah Ibrahim, Lucinda Risi, Lisa M. Hanson, Carolyne Bird, Linda L. Mitchell, Elaine X. Wooton, Donna O. Eisenberg, Thomas W. Vastrick, Marie E. Durina, Kathleen Annunziata Nicolaides, Khody R. Detwiler, Tobin Tanaka, Larry A. Olson, Zain M. Bhaloo, Peter Tytell, Timothy A. Campbell, and Mark T. Goff.  
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ASQDE 2020 Online Conference

ASQDE logoThe 78th Annual General Meeting of the American Society of Questioned Document Examiners (ASQDE, Inc) was held August 10th through 14th, 2020.  It was a new type of meeting necessitated by the COVID-19 pandemic.  The meeting was originally planned to be held in Frankenmuth, Michigan but a (very wise) decision was made to hold an entirely virtual meeting instead.  The theme for this year was “Future-Proofing Questioned Documents”.
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CSFS Position paper on the Logical Approach

I recently published an editorial in the Journal of the Canadian Society of Forensic Science.  Two versions were published almost simultaneously (the original written in English and a translation in French) entitled, respectively, “CSFS Document Section Position on the Logical Approach to Evidence Evaluation and Corresponding Wording of Conclusions” and “La position de la Section des documents de la SCSJ sur l’approche logique de l’évaluation de la preuve et le libellé des conclusions”.

I wrote these in my capacity as the sitting chairman of the Documents section of the CSFS, on behalf of the members of that section.  The impetus for writing them was to introduce the “logical approach” and related topics to the Canadian forensic community in a ‘formal’ way (hopefully resulting in ongoing discussion) and to provide the public and the courts with the perspective of forensic practitioners who have reviewed the literature and studied this issue in depth. To that end, the document references many initiatives relating to the topic. I will note that it’s not a perfect document but it covers the main points reasonably well.

Please note that this position paper was first written a few years ago.  There was considerable delay in publication relating to the production of an acceptable French-language translation of the document. I must thank Julie Binette who was invaluable in that process. The delay, however, means the references provided in the paper are not fully up-to-date with the very latest developments in this area.

Nonetheless, that shortcoming doesn’t detract from the position expressed.  Today there is even more support and justification than is outlined in the paper. 

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Measurement Science and Standards in Forensic Handwriting Analysis Conference

The expression “better late than never” applies to this post. Over the span of two days in June 2013 the Measurement Science and Standards in Forensic Handwriting Analysis (MSSFHA) conference was held. It explored the (then) current state of forensic handwriting analysis, aka, forensic handwriting examination (FHE). Presentations varied in content but most discussed recent advancements in measurement science and quantitative analyses as it relates to FHE.

NIST Forensic logo

The conference was organized by NIST’s Law Enforcement Standards Office (OLES) in collaboration with the AAFS — Questioned Document Section, the ABFDE, the ASQDE, the FBI Laboratory, the NIJ and SWGDOC.

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2016 ASQDE Panel “Approaches to Evaluation and Reporting of Expert Evidence”

Every ASQDE meeting is worth attending. They are great fun with lots of useful and interesting content. Unfortunately, I could not make it to the 2016 ASQDE conference held in Pensacola, Florida.  Nonetheless I managed to participate, albeit via Skype.

2016 ASQDE panel discussion - ASQDE logoOne of the activities at the conference was a panel discussion discussing “Approaches to Evaluation and Reporting of Expert Evidence” and I was invited to participant with three other people. It was a very interesting session…
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Prior odds — their meaning and significance

The concepts of ‘prior odds’, a.k.a., prior probabilities or simply priors, and ‘posterior odds’ come up in most discussions about the evaluation of evidence. The significance and meaning of both terms becomes clear when viewed in the context of a “Bayesian approach”, or the logical approach, to evidence evaluation. That approach has been discussed at length elsewhere and relates to the updating of one’s belief about events based upon new information. A key aspect is that some existing belief, encapsulated as the ‘prior odds’ of two competing possibilities or events, will be updated on the basis of new information, encapsulated in the ‘likelihood-ratio’1 (another term you will undoubtedly have seen), to produce some new belief, encapsulated as ‘posterior odds’ about those same competing possibilities.

But what precisely do these terms, ‘prior odds’ and ‘posterior odds’, mean and how do they relate to the work of a forensic examiner?
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