Texas sharpshooter fallacy

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The Texas sharpshooter fallacy is an

multiple comparisons problem (in statistics) and apophenia (in cognitive psychology). It is related to the clustering illusion, which is the tendency in human cognition
to interpret patterns where none actually exist.

The name comes from a metaphor about a person from Texas who fires a gun at the side of a barn, then paints a shooting target centered on the tightest cluster of shots and claims to be a sharpshooter.[2][3][4]

Structure

A set of 100 randomly generated points displayed on a scatter graph. Examining the points, it is easy to identify apparent patterns. In particular, rather than spreading out evenly, it is not uncommon for random data points to form clusters, giving the (false) impression of "hot spots" created by some underlying cause.

The Texas sharpshooter fallacy often arises when a person has a large amount of data at their disposal but only focuses on a small subset of that data. Some factor other than the one attributed may give all the elements in that subset some kind of common property (or pair of common properties, when arguing for correlation). If the person attempts to account for the likelihood of finding some subset in the large data with some common property by a factor other than its actual cause, then that person is likely committing a Texas sharpshooter fallacy.

The fallacy is characterized by a lack of a specific hypothesis prior to the gathering of data, or the formulation of a hypothesis only after data have already been gathered and examined.

hypotheses suggested by the data
).

Examples

A Swedish study in 1992 tried to determine whether power lines caused some kind of poor health effects.[6] The researchers surveyed people living within 300 meters of high-voltage power lines over 25 years and looked for statistically significant increases in rates of over 800 ailments. The study found that the incidence of childhood leukemia was four times higher among those who lived closest to the power lines, and it spurred calls to action by the Swedish government.[7] The problem with the conclusion, however, was that the number of potential ailments, i.e., over 800, was so large that it created a high probability that at least one ailment would exhibit the appearance of a statistically significant difference by chance alone, a situation known as the multiple comparisons problem. Subsequent studies failed to show any association between power lines and childhood leukemia.[8]

The fallacy is often found in modern-day interpretations of the quatrains of Nostradamus. Nostradamus's quatrains are often liberally translated from their original (archaic) French versions, in which their historical context is often lost, and then applied to support the erroneous conclusion that Nostradamus predicted a given modern-day event after the event actually occurred.[9]

See also

Related fallacies

  • Correlative-based fallacies – Informal fallacies based on correlative conjunctions
  • Cum hoc ergo propter hoc
     – Refutation of a logical fallacy
  • Post hoc ergo propter hoc – Fallacy of assumption of causality based on sequence of events

References

  1. ^ Bennett, Bo, "Texas sharpshooter fallacy", Logically Fallacious, retrieved 21 October 2014, description: ignoring the difference while focusing on the similarities, thus coming to an inaccurate conclusion
  2. ^ Barry Popik (2013-03-09). "Texas Sharpshooter Fallacy". barrypopik.com. Retrieved 2015-11-10.
  3. ^ Atul Gawande (1999-08-02). "The cancer-cluster myth" (PDF). The New Yorker. Retrieved 2009-10-10.
  4. ISBN 0-471-27242-6
    . Retrieved 2012-03-25. The term refers to the story of the Texan who shoots holes in the side of a barn and then draws a bull's-eye around the bullet holes
  5. doi:10.1093/lpr/mgp013
    . Retrieved 2012-03-25. Texas sharpshooter fallacy...this article demonstrates how post hoc target shifting occurs and how it can distort the frequency and likelihood ratio statistics used to characterize DNA matches, making matches appear more probative than they actually are.
  6. PMID 8213751
    .
  7. ^ Coghlan, Andy. "Swedish studies pinpoint power line cancer link". New Scientist.
  8. ^ "Frontline: previous reports: transcripts: currents of fear". PBS. 1995-06-13. Archived from the original on 2016-02-03. Retrieved 2012-07-03.
  9. ^ "Nostradamus Predicted 9/11?". snopes.com. 12 September 2001. Retrieved 2012-07-03.

External links

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