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Availability Heuristic

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Definition:

An availability heuristic is a mental shortcut that relies on immediate examples that come to mind. When you are trying to make a decision, a number of related events or situations might immediately spring to the forefront of your thoughts. As a result, you might judge that those events are more frequent and possible than others. You give greater credence to this information and tend to overestimate the probability and likelihood of similar things happening in the future.

The term was first coined in 1973 by psychologists Amos Tversky and Daniel Kahneman. They suggested that the availability heuristic occurs unconsciously and operates under the principle that "if you can think of it, it must be important." Things that come to mind more easily are believed to be far more common and more accurate reflections of the real world.

For example, after seeing several news reports about car thefts, you might make a judgment that vehicle theft is much more common than it really is in your area. This type of availability heuristic can be helpful and important in decision-making. When faced with a choice, we often lack the time or resources to investigate in greater depth. Faced with the need to an immediate decision, the availability heuristic allows people to quickly arrive at a conclusion.

While it can be useful at times, the availability heuristic can lead to problems and errors. Reports of child abductions, airplane accidents, and train derailments often lead people to believe that such events are much more typical than they truly are.

Examples

  • After seeing news reports about people losing their jobs, you might start to believe that you are in danger of being layed-off. You start lying awake in bed each night worrying that you are about to be fired.

  • After seeing several television programs on shark attacks, you start to think that such incidences are relatively common. When you go on vacation, you refuse to swim in the ocean because you believe the probability of a shark attack is high.

  • After reading an article about lottery winners, you start to overestimate your own likelihood of winning the jackpot. You start spending more money than you should each week on lottery tickets.

Observations

  • "Perhaps the most obvious demonstration of availability in real life is the impact of the fortuitous availability of events or scenarios. Many readers must have experienced the temporary rise in the subjective probability of an accident after seeing a car overturned by the side of the road. Similarly, many must have noticed an increase in the subjective probability that an accident or malfunction will start a thermonuclear war after seeing a movie in which such an occurrence was vividly portrayed. Continued preoccupation with an outcome may increase its availability, and hence its perceived likelihood. People are preoccupied with highly desirable outcomes, such as winning the sweepstakes, or with highly undesirable outcomes, such as an airplane crash. Consequently, availability provides a mechanism by which occurrences of extreme utility (or disutility) may appear more likely than they actually are."
    (Amos Tversky and Daniel Kahneman, 1973, "Availability: A heuristic for judging frequency and probability." Cognitive Psychology, 5(1), 207-233)

  • "The availability heuristic refers to a tendency to form a judgment on the basis of what is readily brought to mind. For example, a person who is asked whether there are more English words that begin with the letter t or the letter k might try to think of words that begin with each of these letters. Since a person can probably think of more words beginning with t, he or she would (correctly) conclude that t is more frequent than k as the first letter of English words."
    (D. L. Medin and B. H. Ross, 1997, Cognitive Psychology, p. 522)

  • "People not only consider what they recall in making a judgment but also use the ease or difficulty with which that content comes to mind as an additional source of information. Most notably, they only rely on the content of their recall if its implications are not called into question by the difficulty that they experience in bringing the relevant material to mind. (Schwarz, Bless, Strack, Klumpp, Rittenauer-Schatka & Simons, 1991, "Ease of retrieval as information: Another look at the availability heuristic." Journal of Personality and Social Psychology, 61(2), 195–202)

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