Texas Sharpshooter
Texas Sharpshooter
Also known as: painting the target after the shot, clustering illusion
Description
The Texas sharpshooter fires at the side of a barn, walks over, and paints a target around the tightest cluster of holes. The fallacy is to select the data that form a pattern after the fact and present the pattern as if it had been predicted. It ignores the misses and the many other patterns that could equally have been drawn.
Form
- A large body of data or events is available.
- Some subset of it, chosen after the event, fits a pattern.
- Therefore the pattern was meaningful, predicted, or caused.
Examples
- A prophecy vague enough to be "fulfilled" by one of a thousand later events, and then credited with foreseeing that one (Biblical Literalism and Inerrancy, Nostradamus).
- The prayer that was answered, selected from all the prayers that were made.
- The dream that came true, recalled because it did; the hundreds that did not, forgotten.
- Cancer clusters identified by looking for them on a map of a large country.
- The "Bible code" and every other search of a long text for hidden messages, which will find them in Moby-Dick too.
Notes
- The cure is to state the prediction, and the criteria for success, before looking at the data. A pattern found afterwards is a hypothesis, not a result, and needs new data to test it.
- Closely related to Confirmation Bias, Survivorship Bias and Cherry-picking, and to the Post Hoc Ergo Propter Hoc error of inferring cause from sequence.