20 September 2010

The Texas Sharpshooter Fallacy

There is a lovely exposition of the Texas Sharpshooter Fallacy on the You Are Not So Smart blog.

It starts off by looking at the coincidences between John F Kennedy and Abraham Lincoln and takes in Nostradamus before moving onto the way we can get fooled into thinking vague and general statements about someone's personality capture who we are and finally ending with a discussion about cancer clusters.


The post is so good I'll leave you with only there main point and a short quote to entice you to read the whole post at You Are Not So Smart blog itself and check out some of the other intriguing posts there as well.

The Misconception: We take randomness into account when determining cause and effect.

The Truth: We tend to ignore random chance when the results seem meaningful or when you want a random event to have a meaningful cause.
“A community that is afflicted with an unusual number of cancers quite naturally looks for a cause in the environment – in the ground, the water, the air. And the correlations are sometimes found: the cluster may arise after, say, contamination of the water supply by a possible carcinogen. The problem is that when scientists have tried to confirm such causes, they haven’t been able to. Raymond Richard Neutra, California’s chief environmental health investigator and an expert on cancer clusters, points out that among hundreds of exhaustive, published investigations of residential clusters in the United States, not one has convincingly identified an underlying environmental cause. Abroad, in only a handful of cases has a neighborhood cancer cluster been shown to arise from an environmental cause. And only one of these cases ended with the discovery of an unrecognized carcinogen.”
The Cancer Cluster Myth, The New Yorker, Feb. 1999

NB: Though I generally agree with the quote above on cancer clusters (where exposure and onset of the health effect is delayed) it is important to remember as the John Snow cholera oubreak cluster mapping image above shows clusters, particularly for acute health impacts, can be very real. In addition, community concerns about cancers and physical health impacts can be a manisfestation of the worry and anxiety communities have about a technology/industrial, the operator of that technology/ industrial facility and the effectiveness of regulatory bodies. And therefore we have a duty to address those concerns.

Image Source: Wikipedia http://en.wikipedia.org/wiki/File:Snow-cholera-map.jpg