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Availability heuristic

Definition:
A heuristic or "rule of thumb" strategy biased for estimating probabilities (of past or future events), based on how easily the related instances of that event come to mind.
 
Example:
Although diseases kill many more people than accidents, it has been shown that people will judge accidents and diseases to be equally fatal. This is because accidents are more dramatic and are often written up in the paper or seen on the news on t.v., and are more available in memory than diseases.
 
Background:
People use heuristics to solve problems or reduce the range of possible answers to questions. Although at times it can result in the correct solution, the availability heuristic can also result in erroneous solutions to problems/questions. In using this rule of thumb, people judge frequency based on a quick count of examples. The use of this strategy is very widespread, and is used in making both trivial and important judgements. People tend to overestimate the frequency of certain rare events if they are dramatic and sensational and underestimate those that are more frequent but occur in private, ordinary situations. This appears to be because the rare, dramatic and sensational events are more easily available in memory.
 
Further Reading:

Hamill, R. Wilson, T. D., & Nisbett, R. E. (1980). Ignoring sample bias: Inferences about populations from atypical cases. (Unpublished manuscript). University of Michigan, Ann Arbor:

Ross, L. (1978). Some afterthoughts on the intuitive psychologist. In L. Berkowitz (Ed.), Cognitive theories in social psychology. New York: Academic Press.

Tversky, A., & Kahneman, D. (1973). Availability: A heuristic for judging frequency and probability. Cognitive Psychology. 5, 207-232.

 
Related Terms:
Representativeness heuristic

Self-Instructional Resources:
Take a 2-item self-test over this concept.

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