Bayesian methods are perfect for forensic and other police
investigations. A couple of books that show how in very different ways
are A Probabilistic Analysis of the Sacco and Vanzetti Evidence (Wiley Series in Probability and Statistics)
and Bayesian Networks and Probabilistic Inference in Forensic Science
. I'm sure there are many, many others.
The New York Times in-house stats-blogger Nate Silver has
tried to write a model analysis using Bayesian thinking of whether the ongoing Swedish sex crimes case against Julian Assange, the personage most widely associated with the Wikileaks website (and whose OKCupid profile you can pruriently find at
http://www.okcupid.com/profile/HarryHarrison), is politically motivated. After starting with a frankly facile argument about whether his fellow passenger on the bullet train in Japan is Japanese, Caucasian, or a combination of the two, Silver goes on to provide not
light, but conspiracy theory heat, about that important question. It
boils down to saying that because he's a high-profile figure who has
annoyed many powerful people, including governments around the world,
that therefore it increases the probability that the current
shenanigans are politically motivated. Therefore, Mr. Silver
concludes, we should be more sceptical that the investigations are
done purely for crime-prevention purposes. The crucial two paragraphs:
What is less ambiguous here, however — as in the case of my bullet
train analogy — is the underlying context. The handling of the charges
suggests that the motivation for bringing them against Mr. Assange is
political. If the motivation is political, then the merits of the
charges might matter less. Even if they fail to result in a
conviction, the authorities might nevertheless succeed in, in essence,
incapacitating Mr. Assange for several months, and preventing him from
releasing further documents through WikiLeaks. They might also injure
Mr. Assange’s reputation among the public: certainly I have learned
more about details Mr. Assange’s personal life in recent days than I
would care to know.
Under these circumstances, then, it becomes more likely that the
charges are indeed weak (or false) ones made to seem as though they
are strong. Conversely, if there were no political motivation, then
the merits of the charges would be more closely related to
authorities’ zealousness in pursing them, and we could take them more
at face value.
Two quick points: Bayesianism doesn't have one right answer; it is
subjectivist. This analysis can be argued over by reasonable people.
I, for one, consider it simplistic. (For example, Silver points out
that the only other Interpol Red Alert against a sex offender issued
by Sweden this year was for a man accused of multiple sexual assaults
against children; a different kettle of pervert-fish indeed. But
what's the denominator? In other words, how many suspects of Swedish
sex crimes were abroad this year at the moment when the Swedes wanted
to talk to them? This is a crucial question without which a useful
likelihood function cannot really be constructed, hence no useful
Bayesian analysis).
But a more important point to make is: so what? Simply because of
Assange's notoriety, according to this analysis, we must conclude that
political motivations are more likely factors for what is going on.
But only a fool would leave it at that and decide the whole case is
suspect, before making a placard and protesting outside the English
courthouses whether Assange will be extradited. Most people would
continue to do what they did before --- i.e. let the legal process
take its course --- and hopefully realise, if they hadn't up until
this point, how incredibly unjust the whole system of European Arrest
Warrants are.
The promotion of Bayesian methods amongst the general public is a joy
to see, but it has to be done rigorously, otherwise laypeople will
justifiably see it as just another way to reinforce one's own
prejudices as opposed to exposing them.
pour encourager les autres.
