Archive for forensics

dodging bullets, IEDs, and fingerprint detection at SimStat19

Posted in pictures, Statistics, University life with tags , , , , , , , , , , , , , , , , , on September 10, 2019 by xi'an

I attended a fairly interesting forensic science session at SimStat 2019 in Salzburg as it concentrated on evidence and measures of evidence rather than on strict applications of Bayesian methodology to forensic problems. Even though American administrations like the FBI or various police departments were involved. It was a highly coherent session and I had a pleasant discussion with some of the speakers after the session. For instance, my friend Alicia Carriquiry presented an approach to determined from images of bullets whether or not they have been fired from the same gun, leading to an interesting case for a point null hypothesis where the point null makes complete sense. The work has been published in Annals of Applied Statistics and is used in practice. The second talk by Danica Ommen on fiducial forensics on IED, asking whether or not copper wires used in the bombs are the same, which is another point null illustration. Which also set an interesting questioning on the dependence of the alternative prior on the distribution of material chosen as it is supposed to cover all possible origins for the disputed item. But more interestingly this talk launched into a discussion of making decision based on finite samplers and unknown parameters, not that specific to forensics, with a definitely surprising representation of the Bayes factor as an expected likelihood ratio which made me first reminiscent of Aitkin’s (1991) infamous posterior likelihood (!) before it dawned on me this was a form of bridge sampling identity where the likelihood ratio only involved parameters common to both models, making it an expression well-defined under both models. This identity could be generalised to the general case by considering a ratio of integrated likelihoods, the extreme case being the ratio equal to the Bayes factor itself. The following two talks by Larry Tang and Christopher Saunders were also focused on the likelihood ratio and their statistical estimates, debating the coherence of using a score function and presenting a functional ABC algorithm where the prior is a Dirichlet (functional) prior. Thus a definitely relevant session from a Bayesian perspective!

 

el lector de cadaveres [book review]

Posted in Books with tags , , , , , , on August 20, 2019 by xi'an

lelecteur-decadavres El lector de cadaveres (the corpse reader) by Antonio Garrido (from Valencià) is an historical novel I picked before departing to Japan as the cover reminded me of van Gulik’s Judge Dee which I very enjoy9788467013849ed (until a terrible movie came out!). Although van Gulik apparently took the idea from a 18th-century Chinese detective crime novel Di Gong An. Anyway, this seemed like a good travel book, although heavy in my hiking backpack. After reading it mostly in the trains, I am not so convinced that it was a great idea! The story stemmed from the author attending a legal medecine conference in Mumbai and hearing of a 13th century Chinese medical expert who could be the very first forensic doctor. The book builds upon this historical character, romancing his early life from destitute to becoming the legal medicine expert of the Song emperor. There are a lot of similarities with Judge Dee in that the meritocratic structure of the Chinese government is central to the central character joining the academy and postulating for the imperial examinations. That the underworld is never far from the ruling classes. That superstition is also a permanent feature in everyday’s life. That cruelty is a part of justice as well as an intricate legal code. And that confucianism is strictly ruling the society, from top to bottom. The historical part is rather nice, with a higher degree of details and apparent authenticity than van Gulik’s. This shows the research undertaken by the author was quite fruitful. The plot however is terrible, with Song Ci falling in every possible trap, trusting every villain in the vicinity and shooting himself in the foot at every occasion. The story goes from one disaster to the next, Ci being only saved by a last minute benevolent passerby. His brilliance as a forensic officer is hard to explain when considering the stupidity he demonstrates all along, while the novel involves several others who also work on the medical analysis of corpses for the courts. A very lengthy suspension of belief!