When an examiner expresses an opinion along the lines of ‘the findings support one proposition over another proposition’, a common question is whether this is means, ‘it is more likely than not that the favored proposition actually happened’?1 Strictly speaking, the short answer to the question is “no, it is inappropriate because these two statements are not equivalent.” In order to conclude the latter, 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 Read more
Many years ago I came across an interesting, if a bit limited, discussion in a blog post entitled “Expert testimony in pattern evidence cases – is absolute uniqueness necessary?”1,2That post is from Sept 4, 2009 just after the publication of National Academy of Science’s report “Strengthening Forensic Science in the United States: a Path Forward”.3 The question posed is still quite relevant today. I would say that most forensic practitioners today would answer the basic question regarding ‘absolute uniqueness’ with a negative response, but their reasons behind that answer applies will still vary.
For many people, ‘absolute uniqueness’ is a ‘forbidden’ concept mostly because of some policy they must follow, or because of a more personal recognition of some (often vague) issue relating to the ‘limits of science’. For other people the issue is a well-defined matter of science and logic, being dictated by the nature of information, what information can tell us about the world, and how information can and should be used to update belief about something. For the latter group (which is steadily increasing in size as awareness and understanding increases), the concept of ‘absolute uniqueness’ is neither required, nor 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 (and I don’t think too much has changed since then). Since the blog itself is no longer active, I have reposted the complete series of posts here (pulling them from archive.org).
The topic started with a post from the moderator:
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.
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.Read more
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.htmlRead more
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!!Read more