representativeness heuristic

n. A model of human decision making in which it is assumed people judge the likelihood that some thing A is in a class B by the similarity of A to B, which is insensitive to prior probabilities and sample size and misconstrues chance events. This leads to viewing chance as a self-correcting process, as in the gambler's fallacy, and an assumption that perceived rare events are normal so that regression to the mean is ignored.