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Bad statistics debunked: serial killers and cervixes

January 22, 2012

If you saw this story going around about how statisticians can predict the activity of serial killers, be sure to read this post by Cosma Shalizi where he brutally tears down the underlying methodology. My favorite part:

Since Simkin and Roychowdhury’s model produces a power law, and these data, whatever else one might say about them, are not power-law distributed, I will refrain from discussing all the ways in which it is a bad model. I will re-iterate that it is an idiotic paper — which is different from saying that Simkin and Roychowdhury are idiots; they are not and have done interesting work on, e.g., estimating how often references are copied from bibliographies without being read by tracking citation errors4. But the idiocy in this paper goes beyond statistical incompetence. The model used here was originally proposed for the time intervals between epileptic fits. The authors realize that

[i]t may seem unreasonable to use the same model to describe an epileptic and a serial killer. However, Lombroso [5] long ago pointed out a link between epilepsy and criminality.

That would be the 19th-century pseudo-scientist3 Cesare Lombroso, who also thought he could identify criminals from the shape of their skulls; for “pointed out”, read “made up”. Like I said: idiocy.

Next, if you’re anything like me, you’ve had way too many experiences giving birth without pain control, even after begging continuously and profusely for some, because of some poorly derived statistical criterion that should never have been applied to anyone. This article debunks that among others related to babies and childbirth.

In particular, it suggests what I always suspected, namely that people misunderstand the effect of using epidurals because they don’t control for the fact that in the case of a long difficult birth you are more likely to get everything, which brings down the average outcome among people with epidurals but doesn’t at all prove causation.

Pregnant ladies, I suggest you print out this article and bring it with you to your OB appointments.

Categories: data science
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