Availability Heuristic Definition
The availability heuristic describes a mental strategy in which people judge probability, frequency, or extremity based on the ease with which and the amount of information that can be brought to mind. For example, people may judge easily imaginable risks such as terrorist attacks or airplane crashes as more likely than the less easily imaginable (but objectively more likely) risks of influenza or automobile accidents.
Context, Consequences, and Causes of Availability Heuristic
Availability was one of three judgmental heuristics (or mental shortcuts), along with representativeness and anchoring and adjustment, that Amos Tversky and Daniel Kahneman hypothesized people adopt to simplify complex judgments. Because information about events that are more likely, frequent, or extreme is typically more available than information about events that are less likely, frequent, or extreme, the availability heuristic typically yields accurate judgments. However, the heuristic can also produce biased and erroneous judgments—as illustrated by people’s perception that terrorist bombings are more risky than influenza—because cognitive availability can be influenced by factors, such as media coverage or vividness, that are unrelated to probability, frequency, or extremity.
Researchers believe that the availability heuristic is partly responsible for several judgmental biases. People who live together, for instance, tend to claim too much responsibility for collaborative efforts such as washing dishes and starting arguments, partly because it is easier for people to think about their own contributions than to think about their cohabitants’ contributions. People also overestimate the magnitude of the correlation between clinical diagnoses (e.g., depression) and invalid diagnostic tests (e.g., drawing a frowning face), because diagnoses and tests that go together are more available than unrelated diagnoses and tests.
Researchers distinguish between two aspects of availability: the amount of information retrieved (e.g., the number of terrorist bombings) and the subjective experience of retrieving information (e.g., the perceived ease with which people can remember terrorist bombings). The amount of information retrieved and the experience of retrieving information often are confounded; that is, information that is more plentifully retrieved is also more easily retrieved. In a series of experiments, Norbert Schwarz and colleagues demonstrated that the experience of retrieving information influences judgments independent of—and sometimes in spite of—the amount of information retrieved. In one experiment, participants were asked to list either three or nine examples of chronic diseases. Participants who listed three examples judged chronic diseases to be more prevalent than those who listed nine examples because listing three examples is easier than listing nine examples even though three is less than nine.
- Schwarz, N., & Vaughn, L. A. (2002). The availability heuristic revisited: Ease of recall and content of recall as distinct sources of information. In T. Gilovich, D. Griffin, & D. Kahneman (Eds.), Heuristics and biases: The psychology of intuitive judgment (pp. 103-119). New York: Cambridge University Press.
- Tversky, A., & Kahneman, D. (1973). Availability: A heuristic for judging frequency and probability. Cognitive Psychology, 5, 207-232.