Understanding the Availability Heuristic
There are occasions in life when we need to try and remember how often we engage in various activities. For instance, a market researcher may wish to know how often we go to the cinema in an average month or a physician may ask how many units of alcohol we consume in an average week. These judgments of frequency may also form the basis for estimating probabilities. For example, the probability of a motorcyclist having a fatal accident can be estimated from the frequency with which fatal accidents occur among motorcyclists. Tversky & Kahneman (1973) proposed that such judgments were made using the availability heuristic.
The availability heuristic—otherwise called Recency Heuristic—is the tendency to judge the frequency or likelihood of an event by the ease with which relevant instances come to mind.
According to Tversky and Kahneman (1973), a person is said to employ the availability heuristic whenever s/he estimates frequency or probability by the ease with which instances or associations could be brought to mind.
The ease with which relevant instances come to mind is influenced not only by the actual frequency but also by factors such as how salient or noticeable the event is, how recent the event is, and whether attention was paid to the event.
To understand this judgment heuristic, it is important to understand that people disproportionately recall the salient events that they have observed; those that are very recent or those that individuals are emotionally involved with in the very recent past are considered more important. The more salient an event is, the more likely the probability that the event will be recalled. The result is that this sort of bias prevents people from considering other potential information and possible related outcomes that may not have occurred recently.
As with heuristics Opens in new window generally, availability can lead to biases. Specifically, Tversky and Kahneman proposed that events that were encountered recently are likely to have a bigger impact on judgment, as are events that one is familiar with, as well as events for which it is easy to construct a vivid mental image.
For example, after the shark horror movie Jaws came out, many people refused to swim in the ocean (and even in fresh water!) because they could not stop thinking about the great white shark in that movie that ate so many unsuspecting swimmers. Few people are actually eaten by sharks, but the movie made the idea of shark attacks highly available in memory, so people overestimated the danger.
Similarly, people overestimate the frequency of dramatic deaths and underestimate the frequency of less dramatic deaths. For example, airplane crash deaths are much more dramatic than are deaths caused by tobacco use, and they get a lot more attention from the mass media, which makes them stand out in memory (high availability). As a result, people think they are common.
In fact, three jumbo jets full of passengers crashing every day for a year would not equal the number of deaths per year caused by tobacco use. Tobacco kills about 6 million people a year. It also takes tobacco a long time to kill a person, so deaths due to tobacco aren’t as salient as deaths due to airplane crashes.
Classic Study of the Availability Heuristic
To demonstrate the effect of the availability heuristic, Tversky and Kahneman conducted a study in which participants were presented with lists of names, where 19 people were famous and 20 were less well known. On half of the occasions the famous people were women and on the other half they were men. Not surprisingly, participants were better at recalling the famous names. However, they also judged the class consisting of the famous names to be more frequent.
The availability heuristic can lead members of a group or team to overestimate their own contribution relative to that of others, because their own contribution comes more easily to mind. Ross & Sicoly (1979) found that husbands and wives tended to overestimate their respective contribution on a list of 20 household activities. An overall measure of perceived responsibility was shown to correlate with the number of self-generated examples of behavior that the individual listed.
Likewise, basketball players on both sides of a match tended to judge their own team as causing the crucial turning point in a game. Ross and Sicoly also showed that attributions of responsibility could be modified by manipulating the participant’s focus of attention. Students who had completed a supervised BA thesis were asked either to assess their own contributions (in percentage terms) or those of their supervisor. The percentage responsibility attributed directly to the supervisor was greater than that attributed indirectly to the supervisor (obtained subtracting the students’ own percentage contribution from 100).