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Situationism describes that changes in human behavior are factors of the situation rather than the traits a person possesses. It began in 1968 when a Person-situation debate was triggered by the publication of a monograph by Walter Mischel.
It refers to an approach to behavior which holds that general traits do not exist (perhaps apart from Intelligence). Behavior, then, is seen as being influenced by external, situational factors rather than internal traits or motivations. It, therefore, challenged the position of trait theorists, such as Hans Eysenck or Raymond B. Cattell.
Situationists based their claims on experiments in which traits such as extraversion were estimated based on behavior in different situations. They found that a particular person's ratings in one situation were not highly predictive of that person's score in another situation. However, in response to such evidence, Hans Eysenck has pointed out that the correlations, while low, are typically still high enough to reach statistical significance. A midrange position, which holds that personality is best understood as resulting from "subtle interplay" of internal and external factors, is known as "interactionism".
Some notable situationist studies include: Zimbardo's Stanford prison experiment, bystander experiments, obedience experiments like Milgram experiment and heat and aggression experiments. The term is popularly associated with Walter Mischel, although he himself does not appear to like the term.