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The clustering illusion is the tendency to erroneously consider the inevitable "streaks" or "clusters" arising in small samples from random distributions to be non-random. The illusion is caused by a human tendency to underpredict the amount of variability likely to appear in a small sample of random or pseudorandom data.


Examples

Thomas Gilovich, an early author on the subject, argued that the effect occurs for different types of random dispersions, including two-dimensional data such as clusters in the locations of impact of
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
V-1 flying bombs on maps of London; or seeing patterns in stock market price fluctuations over time. Although Londoners developed specific theories about the pattern of impacts within London, a statistical analysis by R. D. Clarke originally published in 1946 showed that the impacts of
V-2 rocket The V-2 (german: Vergeltungswaffe 2, lit=Retaliation Weapon 2), with the technical name '' Aggregat 4'' (A-4), was the world’s first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was develop ...
s on London were a close fit to a random distribution.


Similar biases

Using this
cognitive bias A cognitive bias is a systematic pattern of deviation from norm or rationality in judgment. Individuals create their own "subjective reality" from their perception of the input. An individual's construction of reality, not the objective input, ...
in causal reasoning may result in the Texas sharpshooter fallacy, in which when differences in data are ignored and similarities are overemphasized. More general forms of erroneous pattern recognition are '' pareidolia'' and '' apophenia''. Related biases are the '' illusion of control'' which the clustering illusion could contribute to, and '' insensitivity to sample size'' in which people don't expect greater variation in smaller samples. A different cognitive bias involving misunderstanding of chance streams is the gambler's fallacy.


Possible causes

Daniel Kahneman Daniel Kahneman (; he, דניאל כהנמן; born March 5, 1934) is an Israeli-American psychologist and economist notable for his work on the psychology of judgment and decision-making, as well as behavioral economics, for which he was awarde ...
and Amos Tversky explained this kind of misprediction as being caused by the representativeness heuristic (which itself they also first proposed).


See also

* Apophenia * Alignments of random points * Complete spatial randomness *
Confirmation bias Confirmation bias is the tendency to search for, interpret, favor, and recall information in a way that confirms or supports one's prior beliefs or values. People display this bias when they select information that supports their views, ignorin ...
* List of cognitive biases * Numeracy bias *
Poisson distribution In probability theory and statistics, the Poisson distribution is a discrete probability distribution that expresses the probability of a given number of events occurring in a fixed interval of time or space if these events occur with a known ...
* Statistical randomness


References


External links


Skeptic's Dictionary: The clustering illusion

Hot Hand website: Statistical analysis of sports streakiness
{{Hidden messages Cognitive biases Statistical randomness Illusions Cluster analysis