Practical Issues when applying the logical approach to FDE work

Applying the logical approach to evidence evaluation in forensic work can be a challenge. I am the first person to admit that is the case. However, I would argue that (1) a challenge is not something to be avoided — it’s something to take on, and (2) the traditional way of doing things is not easy — it too is a challenge. In fact, it is very important to understand that the logical approach is no more difficult or challenging than what has always been done by forensic document examiners. Indeed, in many ways it is simpler and more straight-forward than our ‘traditional’ approach to such things. This post will touch upon some of the practical issues faced by examiners when applying the logical approach to FDE work.

After studying and using this approach for some time I can assure you that it is not a particularly difficult approach to apply. In select aspects it differs from the traditional approach and, as a result, it feels unfamiliar. Often, this relates to the need to consider things more fully; giving consideration to things we tend to ‘quickly assess’ (or dismiss) when using the traditional approach. But it does not change most things that we do. In fact, it primarily affects the evaluation element of the work; not the elements of analysis or comparison. It requires a different way of thinking about the evaluation process which starts with the focus of the evaluation.

The earliest workshops I presented on this topic were focused, for the most part, on the theory and philosophical bases of the approach, plus the benefits of using it. I did not try to delve into the practical side of things, mainly due to time constraints, but also because I was simply trying to convey its value. FDE’s are, however, a practical lot so I feel that my approach has had limited impact. The most common feedback has been, “I can’t see how it will work in practice…”

That is a fair enough criticism, all things considered. More recently, I have been involved in workshops designed expressly for hands-on practice — after all, there really is nothing like hands-on activities to make something real and tangible. More of those workshops are needed, but they are time-consuming to create. For now, here are some thoughts on these issues deriving mainly from feedback received to date during those workshops.

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ICFIS 2023

The 11th International Conference on Forensic Inference and Statistics, or ICFIS 2023, is set for June 12-15 of this year. It will be held at the Faculty of Law (Juridicum) of Lund University, Lund, Sweden. While I am saddened that I cannot attend this particular meeting, several years ago I had the pleasure of going to the 2014 International Conference on Forensic Inference and Statistics, or ICFIS which was the 9th iteration of the conference. I wrote a blog post about that meeting some time ago.

I can say, based on past experience alone, that this meeting is well worth attending. That’s particularly true if you are interested in the logical approach to evidence evaluation, but it would benefit any forensic scientist. You will not find a better collection of brilliant people all focused on forensic inference, in the broadest sense.

Forensic scientists, lawyers, academics—they will all be there.

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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 favoured 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.3Read more

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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Is Absolute Uniqueness Necessary?

Many years ago I came across an interesting, if limited, discussion in a blog post entitled “Expert testimony in pattern evidence cases – is absolute uniqueness necessary?”1,2 That post is dated Sept 4, 2009, shortly after the publication of National Academy of Science’s report “Strengthening Forensic Science in the United States: a Path Forward”.3 But the basic question posed in it is still relevant today. I would say that most forensic practitioners today would answer the question about the necessity of ‘absolute uniqueness’ in the negative. However, their individual reason(s) for their answer will still vary.

For many people, ‘absolute uniqueness’ is mainly a ‘forbidden’ concept because of some policy they must follow, or because of a more personal recognition of an (often vague) issue relating to the ‘limits of science’. For other people the matter is a well-defined issue in science and logic dictated by the nature and limits of information (knowledge), what information can really tell us about the world, and how information can and should be used to update beliefs about the world. For the latter group (which is steadily increasing in size as awareness and understanding improves), the concept of ‘absolute uniqueness’ is neither required, nor even beneficial in forensic work.

There has been a LOT of discussion about this in recent years, but I found the blog post interesting at the time even though it focused mainly on latent print examination. I feel that not much has changed since then so, even now, it deserves recognition and consideration.  Since the blog itself is no longer active, I have reposted the complete series of messages here (pulling them from

The topic started with a post from the moderator (Barry Fisher) who wrote:

Expert testimony in pattern evidence cases – is absolute uniqueness necessary?
What information is needed to form a conclusion about an identification? Do conclusions require statistical data, as in DNA cases, to offer an opinion? Is it possible to state that two items of evidence come from a sole source? What may an expert opine when no statistical data is readily available and only experience suggests a conclusion? The National Academy report raises some profound questions and some intriguing research possibilities. But in the interim, while we wait for academics to study the multitude of pattern evidence forensic scientists encounter in their day to day work, who may report cases and testify in court? Readers are invited to speak to these issues.

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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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Book announcement: Forensic Examination of Signatures

Forensic Examination of Signatures CoverI was pleased be a co-contributor for Dr. Linton A. Mohammed’s latest textbook, Forensic Examination of Signatures.  Other contributors, along with Dr. Mohammed, were Lloyd Cunningham, William Flynn, and Kathleen Nicolaides, with the Foreword by the esteemed Professor David Kaye.  The text was published June 6, 2019 by Elsevier’s Academic Press (ISBN:  978-0-12-813029-2,

The book focuses on the forensic examination and evaluation of signatures which is one of the most difficult areas of Forensic Document Examination.  My contribution was Chapter 11 entitled “Conclusions, Reporting and Testimony”, co-written with Dr. Mohammed.
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Human Factors in Forensic Handwriting Examination


One of the projects I had the pleasure to be involved in was the “Expert Working Group for Human Factors in Handwriting Examination”. The WG was convened in 2015 to conduct a scientific assessment of the effects of Human Factors in Forensic Handwriting Examination, with the support of the National Institute of Justice (NIJ) Office of Investigative and Forensic Sciences (OIFS) and the National Institute of Standards and Technology (NIST) Special Programs Office.

It was a lengthy process involving a lot of people drawn from many different domains. The authors of the report included Melissa K. Taylor, Carolyne Bird, Brett Bishop, Ted Burkes, Michael P. Caligiuri, Bryan Found, Wesley P. Grose, Lauren R. Logan, Kenneth E. Melson, Mara L. Merlino, Larry S. Miller, Linton Mohammed, Jonathan Morris, John Paul Osborn, Nikola Osborne, Brent Ostrum, Christopher P. Saunders, Scott A. Shappell, H. David Sheets, Sargur N. Srihari, Reinoud D. Stoel, Thomas W. Vastrick, Heather E. Waltke, and Emily J. Will.

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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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Interesting and Useful Stuff

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Forensic Document Examination is a complex area involving many different topics and abilities. I am always looking for useful resources that can help me do this work and some of that information can be found online.

In time I would like to provide a more fulsome list of online resources pertaining to the different facets of this work but that is going to take a while to compile and it will be an ongoing project. Still there are already a few websites I consider to be particularly interesting and useful. I’ve compiled them into a list to serve as a starting point for a more complete and general list.

Some of these relate to Forensic Document Examination, some to logic and reasoning, and some pertain to programming and statistics (i.e., my main areas of interest). They are not listed in any particular order. Other categories, and more sites, may be added from time to time. In the meantime, I hope that you find them as interesting and useful as I have. If you know of other sites that you think might be included here, please let me know via the contact page. Enjoy!!

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