Originally posted by JeffHamm
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Reading expert opinions can sometimes require it's own expertise! Experts phrase things in ways that can sometimes sound very different to the untrained ear. For example, even if their opinion is on the "you may draw this conclusion safely ...", they will phrase things in terms of "it is highly probable" or "highly improbable" ... leaving the untrained ear to presume the expert is saying there is reasonable room for the alternative. Generally, that's not going to be the case and the expert is simply acknowledging that given the nature of any data analysis, nothing is 100%, and so we phrase things that way because we are trained to phrase things that way.
When an expert spends a lot of time pointing out that the data they have been given to work with is not sufficient (i.e. I would require original material, not images, etc), then they are indicating that what follows is not their expert opinion on the matter, rather, they are simply being polite and trying to suggest what such an analysis might show, if they indeed had the proper, and sufficient amount, of material to do an analysis upon.
Finally, it is not uncommon for people to think that experts will always offer an opinion of "yay or nay", but there is a third, often more common opinion that emerges, which is in between - that's the "equivocal" outcome, meaning it is unclear if the answer should be yay or if it should be nay, as the evidence could fit either of those. It's not sufficient to determine. So where he is talking about "can not be ruled out", he's indicating that such a phrase is an expression from the "equivocal outcome"; it can't be ruled out does not mean it has been ruled in. We are in that grey area of either is possible.
Given he clearly indicates that the material he working from is not such that he could (or will) form an expert opinion, and that he goes on to try and explain how saying "can not be ruled out" simply means that "there are obvious likenesses in certain respects", which is a far cry from saying "the similarities are such that we can be confident the same hand has a high probability of the being source of both signatures" (the latter being a phrase one might seen if an expert was of the opinion there was a match, the former being an indication of non-committal opinion).
I have no experience with handwriting analysis myself, but have lots of experience with expert opinions and how we phrase things (I'm an expert in some areas of research, most of which bear little relevance to criminology, but expert language is a function of how we're trained to talk about data, and analysis, and statements based upon the probabilities derived from statistical analysis and so forth, so I feel somewhat confident in sharing my thoughts here). Researchers are a funny lot, and we end up with idiosyncratic ways of expressing things that can easily be misinterpreted by those not dealing with data and statistical analyses on a day-to-day basis.
And also, that training, and how experts "speak", has changed since the 1800s of course. Experts were expected to speak in more definite language, but over time, things have shifted to use language that more accurately reflects the fact that even if the analysis leads you to be 99% sure, you cannot say definitely, because, 1% error means you're wrong 1% of the time after all, while definitely implies there's 0% room for error - that you cannot be wrong. In such a case, the expert would resort to describing things something like "In all reasonable probability the two items were written by the same hand", but if questioned by a defence lawyer, they would have to admit that "Yes, there is a 1% chance that the signatures were written by two different people", and it would be the jury that would have to decide if 1% was reasonable doubt.
- Jeff
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