The availability heuristic is a phenomenon (which can result in a cognitive bias) in which people predict the frequency of an event, or a proportion within a population, based on how easily an example can be brought to mind. This phenomenon was first reported by psychologists Amos Tversky and Daniel Kahneman, who also identified the representativeness heuristic. To see how availability differs from related terms vividness and salience, see availability, salience and vividness.
The Availability heuristic is gauging what is more likely based on vivid memories. The problem is individuals tend to remember unusual events more than everyday, commonplace events. For example, airplane crashes receive lots of national media coverage. Fatal car crashes do not. However, more people are afraid of flying than driving a car, even though statistically airplane travel is safer. Media coverage feeds into this bias; because rare or unusual events such as medical errors, animal attacks and natural disasters are highly publicized, people perceive these events as having a higher probability of happening.