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When is a ‘Bayesian’ not a ‘Bayesian’?

Several of the posts on this blog relate to the logical approach to evidence evaluation; aka, the coherent logical approach, or the likelihood-ratio (LR) approach. In my opinion, it is the best way to evaluate evidence for forensic purposes no matter what type of evidence is being discussed. I say “best” because it is simple, logically sound, and relatively straight-forward to apply in forensic work.  It helps to promote transparency through the application of a thorough and complete evaluation process (all points I have explained in other posts).

The reality is, however, that this approach is still not well understood by forensic practitioners, nor by members of the legal profession.

I hope that in time, and with education, that will change. Several workshops I have presented have been aimed at helping examiners understand what it really means, how it works, the philosophical basis behind the approach as well as the need for and benefit of doing things that particular way. It really does work to the benefit of both the examiner and their ultimate client, the court.

One recurring issue at these workshops relates to the very basic and fundamental concept of what the term “Bayesian” means. For various reasons, but mainly just misunderstanding, many people in the forensic document examination community hold the term “Bayesian” in negative regard. When the word ‘Bayes’, or any of its many derivations, come up in the conversation eyes glaze over while heads sag ever so slightly. And those are the positive people in the crowd.

I find such reactions understandable, but unfortunate.  The fact is that an understanding of the term is beneficial for anyone interested in how it might be applied in a forensic evidence context, whether or not one chooses to do so.  Indeed, for myself the answer to the question posed above — when is a Bayesian not a Bayesian? — lies in knowing how the overall Bayesian philosophy and theorem (or rule) differs from the more constrained and limited logical approach to evidence evaluation. These two are not the same or even close to equivalent.

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The ‘best’ textbook ever written about forensic handwriting identification…

Huber and Headrick Handwriting Identification

Okay, determining the ‘best’ of anything is always a challenge. It is, in almost every instance, a highly subjective decision based on some set of appealing features or characteristics… appealing to the person making the determination, of course. And, because this is my blog, that person happens to be me. In fairness, there are a number of authors who have written extensively on the topic: Osborn, Ellen, Hilton, Harrison, Hilton, among others (and I apologize to those I have left off this list). I have read all of those textbooks (including most editions) and each has its strengths and weaknesses. Nonetheless, in my opinion the best general textbook written to date on the topic of handwriting identification was done by co-authors Roy A. Huber and A.M. (Tom) Headrick, both long-time document examiners in the R.C.M. Police laboratory system.

That textbook is Handwriting Identification: Facts and Fundamentals.1Read more

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Can of worms…

Worms in a can

When someone “opens a can of worms” it usually spells trouble. For many people, that phrase evokes a powerful image of a writhing mess of worms escaping from a previously-sealed, but now opened, can or container. With the result of such action being serious problems for the owner of said can, often problems of an unanticipated or uncertain nature. In the context of our work as Forensic Document Examiners, I sometimes hear this coming up in discussions of how to handle questions on the stand. The advice goes along the lines of ‘keep your answers simple and say as little as possible in order to limit any opportunity for questions from the other side.’

It is suggested that lengthy or complex answers will only lead to more questions and more discussion. The latter are the proverbial “can of worms” that one must strive to avoid opening.

That makes little sense to me.

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2014 ASQDE-ASFDE Panel Discussion “Conclusions…”

The 2014 ASQDE–ASFDE conference included an interesting panel discussion with the title “Conclusions… Signature and Handwriting Conclusion Terminology and Scales”. I was fortunate to be able to take part, albeit only remotely via Skype.

ASQDE ASFDE logos

 

The abstract for the session was as follows:

A current and global issue in our field is the topic of conclusion terminology and conclusion scales, particularly in respect of signature and handwriting conclusions. It is an important yet difficult topic to address because, while there is some commonality in the conclusion scales used in different geographical regions around the world, within a number of geographical regions there are multiple scales in use. It is for this very reason that it is also a topic in great need of discussion and there is a strong argument that we should attempt to reach a consensus (even if the result is that we agree to disagree).

This panel discussion is a collaboration of insights from numerous colleagues in our field in person, via Skype and in writing from private and government laboratories in geographical regions across the Americas, Australia, Asia, Africa, the Middle East and Europe.
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R. v. Mohan — Canada’s Daubert?

It is safe to say that pretty much everyone working in the forensic sciences has heard of the Daubert ruling or, more specifically, Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993).2 It was a pivotal ruling that, together with two subsequent rulings General Electric Co. v Joiner, 522 U.S. 136 (1997)3 and Kumho Tire Co., Ltd. v Carmichael, 526 U.S. 137 (1999),4 has greatly affected many legal jurisdictions in the United States. And, as is often the case, whatever happens in the USA tends to have influence elsewhere.

R. v. Mohan — Canada's Daubert

Shortly after that, in Canada, there was a key Supreme Court ruling that addressed admissibility of forensic expertise — R. v. Mohan, [1994] 2 S.C.R. 9.5

That ruling laid out the test for the admissibility of ‘novel’ expert evidence (see Mohan, page 4) in Canada.

Subsequently, the factors explained in that ruling have been applied, just as those in Daubert were, to many types of traditional forensic science evidence. It is, perhaps, rather ironic that rulings intended to liberalize the admission of new (and potentially) helpful evidence would lead to challenges of all forms and types of evidence.

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ICFIS 2014 — Teaching the Logical Approach for Evidence Evaluation to FDEs

This year’s International Conference on Forensic Inference and Statistics (ICFIS) is being held at Leiden University in the Netherlands.  ICFIS 2014 logoICFIS conferences are always very good and this is the 9th such event.  I am hoping to attend to present my thoughts on the topic of education relating to the logical (a.k.a. likelihood-ratio or LR) approach to evidence evaluation. Over the last few years I have given several one and two-day seminars and workshops on this topic, mainly for Forensic Document Examiners (FDEs) though the subject matter relates to all disciplines equally.  Those workshops have been great and provided a relatively unusual opportunity to learn about how fully trained examiners come to grips with a complicated and difficult topic.  One that is fundamental to FDE work.
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R script for viewing Topaz digital signature files

During the 2013 ASQDE conference I had the pleasure to participate in a workshop by Bill Flynn and Kathleen Nicolaides entitled “Forensic Examination of Digital Signatures”.6 The workshop covered various topics but one part of it involved the production of visual graphs representing digital signature data which was done using a spreadsheet program (MS Excel).  A spreadsheet works well for many things but, for this purpose, it was both tedious and unnecessary.

I decided to take a few minutes to write a semi-automated routine that would run in “R”, free open-source software that does this sort of thing very well.  Please note that the routine has not been updated since it was first written in 2013, however it should still work for Topaz data (.sig) files.

The routine is available, with some restrictions and caveats, to qualified forensic document examiners and interested researchers / academics. If you would like to get a copy of it, please contact me using the form shown below. Please include enough bio information for me to assess your request and I will get back to you.

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Tobin Tanaka at the CIS conference, Richmond BC

My colleague and fellow document examiner, Tobin Tanaka, is giving a presentation about Forensic Document Examination at the Canadian Identification Society (CIS) Annual Educational Conference at the River Rock Casino in lovely Richmond, BC.

A full review of the conference will be provided at some time in the future but, for now, Tobin has asked me to provide links to his presentations so that attendees have access to his talk in electronic format.

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Statistics — Worse than a lie

It has oft been said that “there are three kinds of lies: lies, damned lies and statistics”.  That phrase, according to Mark Twain, came from Benjamin Disraeli. Interestingly, it has never been found in Disraeli’s written works so that attribution is likely incorrect.

A lie, perhaps, by Twain?

Lies - Mallett

But I digress.  The source of the statement doesn’t really matter.  It is enough that the phrase reflects the belief that many people have when they think about statistics.7

It is a catchy little phrase.  Yet most reasonable people know that numbers — and statistics are simply numbers after all — cannot do anything on their own.  Hence, statistics can no more lie than they can sing or dance.

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ASQDE “Conclusions and Logical Inference” Workshop 2013

This year the Annual General Meeting of the American Society of Questioned Document Examiners (ASQDE) ASQDE 2013 is being held in Indianapolis, Indiana on August 24 through 29, 2013. In keeping with the theme, “Demonstrative Science: Illustrating Findings in Reports and Court Testimony”, I will be presenting a one-day workshop entitled “Conclusion Scales and Logical Inference” on Sunday, August 25.
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