Clustering Illusion

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The clustering illusion refers to the tendency to erroneously perceive small samples from random distributions as having significant ‘streaks’ or ‘clusters,’ caused by a human tendency to underpredict the amount of variability likely to appear in a small sample of random or semi-random data due to chance. Illusionary clusters were found in the locations of impact of V-1 flying bombs on London during World War II and as streaks in stock market price fluctuations over time.

The clustering illusion was central to a widely reported study by Gilovich, Robert Vallone and Amos Tversky. They found that the idea that basketball players shoot successfully in ‘streaks,’ sometimes called by sportcasters as having a ‘hot hand’ and widely believed by Gilovich et al.’s subjects, was false. In the data they collected, if anything the success of a previous throw very slightly predicted a subsequent miss rather than another success. Using this cognitive bias in causal reasoning may result in the Texas sharpshooter fallacy. It may also have a relationship with gambler’s fallacy. More general forms of erroneous pattern recognition are pareidolia and apophenia.


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