259)īut was Venn really the first to come up with this story? The alternative expression mentioned by Thompson, “painting the target around the arrow”, suggests that the anecdote predates the invention of gunpowder. A deception analogous to this is, I think, often practised unconsciously in other matters.” (Venn, 1866, p. The shot had really been aimed in a general way at the barn door, and had hit it the target was afterwards chalked round the spot where the bullet struck. His statement was true enough, but he suppressed a rather important fact. A man once pointed to a small target chalked upon a door, the target having a bullet hole through the centre of it, and surprised some spectators by declaring that he had fired that shot from an old fowling-piece at a distance of a hundred yards. (…)Īn illustration may serve to make this plain. This consists in choosing the class to which to refer an event, and therefore judging of the rarity of the event and the consequent improbability of foretelling it, after it has happened, and then transferring the impressions we experience to a supposed contemplation of the event beforehand. “One of the most fertile sources of error and confusion upon the subject has been already several times alluded to, and in part discussed in a previous chapter.
Although Venn’s views on statistical inference and the nature of probability were deeply misguided –he was one of the first frequentists and hence carries part of the blame for creating the current epistemological wastelands– he did do other work that was useful not only is he responsible for the Venn diagrams, but Wikipedia informs us that he also constructed a machine for bowling cricket balls.īelow is the relevant fragment, taken from Venn’s book “The logic of chance” (1866): Who first described the scenario? An early reference points to John Venn. The origin of the “legendary Texan” is somewhat of a mystery. The kind of post hoc target fixing illustrated by this story has also been called painting the target around the arrow. Because the sharpshooter was able to fix the targets after taking the shots, the evidence of his accuracy was far less probative than it appeared. Of course, their reasoning was fallacious. The neighbours were impressed: they thought it was extremely improbable that the rifleman could have hit every target dead centre unless he was indeed an extraordinary marksman, and they therefore declared the man to be the greatest sharpshooter in the state.
When the paint dried, he invited his neighbours to see what a great shot he was. The name is derived from the story of a legendary Texan who fired his rifle randomly into the side of a barn and then painted a target around each of the bullet holes. “The Texas sharpshooter fallacy is the name epidemiologists have given to the tendency to assign unwarranted significance to random data by viewing it post hoc in an unduly narrow context (Gawande, 1999). The Texas sharpshooter is commonly introduced without a reference to its progenitor.įor instance, Thompson (2009, pp. The sharpshooter symbolizes the dangers of post-hoc theorizing, that is, of finding your hypothesis in the data.
The infamous Texas sharpshooter fires randomly at a barn door and then paints the targets around the bullet holes, creating the false impression of being an excellent marksman. The picture of the Texas sharpshooter is taken from an illustration by Dirk-Jan Hoek (CC-BY).
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