## Math on Trial, by Leila Schneps and Coralie Colmez

The arithmetic geometer Leila Schneps, who taught me most of what I know about Galois actions on fundamental groups of varieties, has a new book out, Math on Trial:  How Numbers Get Used and Abused in the Courtroom, written with her daughter Coralie Colmez.  Each chapter covers a famous case whose resolution, for better or worse, involved a mathematical argument.  Interspersed among the homicide and vice are short chapters that speak directly to some of the mathematical and statistical issues that arise in legal matters.  One of the cases is the much-publicized prosecution of college student Amanda Knox for a murder in Italy; today in the New York Times, Schneps and Colmez write about some of the mathematical pratfalls in their trial.

I am happy to have played some small part in building their book — I was the one who told Leila about the murder of Diana Sylvester, which turned into a whole chapter of Math on Trial; very satisfying to see the case treated with much more rigor, depth, and care than I gave it on the blog!  I hope it is not a spoiler to say that Schneps and Colmez come down on the side of assigning a probability close to 1 that the right man was convicted (though not nearly so close to 1 as the prosecution claimed, and perhaps to close enough for a jury to have rightfully convicted, depending on how you roll re “reasonable doubt.”)

## Dead people are not numerators

One more thing about the Steven Pinker interview in the Guardian, previously kvetched about here in October.  The interview leads with a very strange table, which lists mass killings (mostly wars, with a sprinkling of famines and non-state-certified genocides) and ranks them by “Death Toll (2oC equivalent.)  “The table takes past conflicts and tyrannies,” the Guardian explains, “and recalibrates their death tolls so their scale can be compared directly.”  In other words, you take the total death toll and you divide by the world population at the time; a single murder two thousand years ago is the equivalent, in this sense, of a 20-person killing spree now.

Bad idea!  I wrote in Slate a while ago about the folly of computations of this kind — in particular, why killing one Israeli is not the “equivalent” of killing 47 Americans.

(Not to mention the fact that the table asks us to compare “The Middle East Slave Trade,” which took 1200 years to rack up its total of 132 million “20th century deaths” (constituting 18m actual slaves), to World War II, which killed its 55m in half a decade.)

None of which is meant to argue against the thesis of Pinker’s book, which seems pretty uncontroversial.   I haven’t read it, but there’s no doubt that Pinker has access to, and uses, more sophisticated quantitative methodology than dividing one number by another and calling it a day.

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