Posted on by RB Ostrum

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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Posted on by RB Ostrum

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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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 archive.org).

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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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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David H. Kaye’s “Forensic Science, Statistics & the Law” Blog

David H. Kaye (DHK) is one of my favourite writers. He is truly prolific and always manages to provide great insights for the reader. His grasp of statistics, logic, and the law is second-to-none, and his ability to communicate those very challenging topics to his audience is equally impressive.

As a mini introduction, David “…is Distinguished Professor, and Weiss Family Scholar in the School of Law, a graduate faculty member of Penn State’s Forensic Science Program, and a Regents’ Professor Emeritus, ASU.” If you would like to see a list of his publications check out http://personal.psu.edu/dhk3/cv/cv_pubs.html 

Yes, DHK has written many things on many topics.1  But I would like to focus on his less formal writings from his blog  Forensic Science, Statistics & the Law.

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Interesting and Useful Stuff

Pen scribble image

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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Posted on by RB Ostrum

CSFS 2018 Conference

The Canadian Society of Forensic Science (CSFS) is holding its 2018 conference and AGM in Gatineau, QC. I’m happy about that because it’s in my own backyard, so to speak.

CSFS conferences vary in their quality and content but this year is looking pretty good.  For example,  the keynote speaker is Dr. Claude Roux whose presentation is entitled ‘Will Forensic Science Reach the End of the Crossroads Soon?’  That’s a tremendous question.  How would you answer it?  Dr. Roux is sure to have an interesting perspective to share with us.  Read more

Posted on by RB Ostrum

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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