Mathematical Malpractice: Spree Killings Again  This analysis,
which claims that the US has more school spree killings than 36
nations combined, is getting a lot of play. It shouldn’t. It is
extremely bad mathematical malpractice.  The basic reason it is
mathematical malpractice is the same reason the Mother Jones
study was: it is difficult to analyze extremely rare events.
When you narrow your investigation to events that happen maybe
once a decade and are compiled haphazardly, you are simply going
to be dominated by small number statistics and selection bias.
You can therefore use those numbers to say, basically, anything
you want.  Let’s break down just how bad the numbers are being
twisted here.  1) The sample ends in 2009. That excludes the
recent spate of knife attacks in Chinese schools that have left
21 dead. If you did this analysis a week ago, you would have had
to drop China from the right column.  2) The sample excludes
acts of terror or war. But if Islamists shoot up a school
because they don’t w