Availability Heuristic

Amos Tversky and Daniel Kahneman described it in the early 1970s as one of the basic heuristics of judgement. It is a case of substitution: the hard question, how often does this happen, is replaced by an easy one, how quickly can I think of an example? Often the two go together, because common things are easier to recall. But ease of recall is also driven by things that have nothing to do with frequency: a dramatic news story, a recent event, something that happened to you or to someone you know. That is why risks that make headlines feel larger than quiet, common ones, and why people tend to buy insurance after a disaster rather than before it. The heuristic distorts fairness too. Kahneman reports that when spouses estimate their own share of the household work, the two shares add up to more than the whole, because each remembers their own efforts far more easily than the other's. Even the feeling of ease counts: in a well-known study, people asked to list many examples of their own assertive behaviour, a hard task, ended up rating themselves less assertive than people asked for only a few. When a judgement about frequency matters, count instead of recalling.