The availability heuristic is a mental shortcut in which people estimate the likelihood of an event by the ease with which examples come to mind. If instances are readily recalled, the event is judged common; if they are hard to recall, it is judged rare.

The heuristic works well when ease of recall actually tracks true frequency. It misleads when vividness, recency, or media coverage makes certain events artificially easy to retrieve. Airplane crashes are rarer than car accidents, yet many people fear flying more than driving because crashes receive intense coverage. After a highly publicized crime, estimates of local crime rates often rise even if the statistics have not changed.

The bias appears in medical diagnosis, financial forecasting, and everyday risk assessment. People can reduce its influence by deliberately seeking base-rate information and by asking whether the examples that come to mind are representative or merely memorable.

Availability is a useful cue, but it is not the same as actual probability.