The representativeness heuristic is a mental shortcut that judges the likelihood of an event by comparing it to a mental prototype of the event. Amos Tversky and Daniel Kahneman first described this particular type of heuristic in the 1970s.
Heuristics are used to help people make decisions more quickly. Although this can be helpful, it can also create cognitive biases. The representativeness heuristic can cause an overestimation of the likelihood of an event, because something being representative of an event does not mean the event itself is more likely to occur.
According to About.com, Tversky and Kahneman conducted an experiment that demonstrated this type of heuristic by describing to a group of research participants a man who was highly intelligent, lacked creativity, and liked order, clarity, and neat, tidy systems. He also had dull, mechanical writing, used corny puns, was competent and had trouble interacting with others. Participants in the study were likely to believe that this man was an engineering major despite the fact that the school had a relatively small number of engineering majors.
In addition, Roy F. Baumeister and Brad J. Bushman described the representative heuristic by pointing out that people tend to believe that in a series of 10 coin flips getting all heads is less likely than getting a mixture of heads and tails, even though both events are equally likely.