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The Texas-sharpshooter fallacy is the name epidemiologists give to the clustering illusion. Politicians, lawyers and some scientists tend to isolate clusters of diseases from their context, thereby giving the illusion of a causal connection between some environmental factor and the disease. What appears to be statistically significant (i.e., not due to chance) is actually expected by the laws of chance.
Of the thousands of studies of cancer-clusters investigated by scientists in the United States, "not one has convincingly identified an underlying environmental cause" (Gawande).
The term refers to the story of the Texas sharpshooter who shoots holes in the side of a barn and then draws a bull's-eye around the bullet holes. Individual cases of disease are noted and then the boundaries are drawn (Gawande).
Gawande, Atul. "The Cancer-Cluster Myth," The New Yorker, February 8, 1999, pp. 34-37.
Gilovich, T., R. Vallone, and A. Tversky. "The hot hand in basketball: On the misperception of random sequences," Cognitive Psychology, 17, 295-314.