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 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

Is Absolute Uniqueness Necessary?

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 Since the blog itself is no longer active, I have reposted the complete series of posts here (pulling them from archive.org).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.

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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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