Clustering Illusion

The clustering illusion is the tendency to perceive meaningful clusters, streaks or patterns in small samples of random data, when the apparent pattern is actually consistent with pure chance. It is closely related to the broader tendency toward apophenia and to the gambler's fallacy, and it was documented influentially by the psychologists Thomas Gilovich, Robert Vallone and Amos Tversky in a 1985 study of perceived "hot hand" shooting streaks in basketball, which found that the run patterns present in actual shooting records were statistically indistinguishable from chance despite players, coaches and fans strongly believing in genuine hot and cold streaks. The effect is attributed to a general human difficulty in correctly judging what a genuinely random sequence should look like, since truly random sequences often contain streaks and clusters that are mistakenly interpreted as evidence of an underlying nonrandom cause.