Kahneman and Tversky spent 1971-72 at the Oregon Research Institute, studying what they called the “availability heuristic.” This heuristic describes the thought process that people use when they estimate the frequency of a category, like “people who divorce over the age of 60.” They often judge frequency by the ease with which instances of that category come to mind.
The availability heuristic is an example of people’s overestimation and overreliance on their own experience when estimating a category. In this example, someone who got divorced over the age of 60 would likely overestimate that category because they put too much weight in their own experience.
Kahneman and Tversky considered how many instances must be retrieved to get an impression of ease. The answer is none. If presented with the strings of letters “XUZONLCJM” and “TAPCERHOB” we immediately know, without generating any instances, that far more words can be constructed with the second string of letters.
The availability heuristic also relies on System 1, because we understand ease automatically and intuitively—as readers can experience by looking at the two strings of words that Kahneman provides.
The availability heuristic substitutes the question “how frequent or how sizeable is this category?” with “how easily can I think of examples of this category?” Events that attract attention (like celebrity divorces), dramatic events in the news (like plane crashes), and personal experiences, pictures, and vivid examples will all alter our sense of how frequent they are.
This substitution is again automatic in order to make our thought process easier. The examples that Kahneman gives demonstrates our mistaken overestimation of things that we have experienced or recently witnessed or heard about.
The availability heuristic explains why we overestimate our own contributions to group activities. When spouses are asked to estimate the percentage of the housework that they do, their responses usually add up to more than 100%.
In this example as well, people rely too much on their own experiences and ignore the fact that they are often not privy to the work that their spouse may have contributed.
In the early 1990s, German psychologists led by Norbert Schwarz studied how people’s impressions of frequency are affected by requirements to come up with specific examples of that category. They asked people to list six (or, in another group, twelve) instances in which they behaved assertively, and then to evaluate how assertive they are. They wanted to see whether people would base their evaluation on the number of examples they could come up with, or the ease with which they could come up with them. The results yielded a clear-cut winner: people who had listed twelve instances rated themselves as less assertive than people who listed six.
The results that the German psychologists found show how much we base our judgments on cognitive ease. Earlier, this principle showed that our tendency toward cognitive ease allowed us to be lazy. Here, the fact that people are not able to experience cognitive ease (in having to come up with many example of their assertiveness) leads them to believe that they must not be assertive because it is difficult to come up with those examples.
This result is paradoxical, and it is due to the strain of coming up with more examples. When Schwarz provided an explanation for the difficulty (i.e., by telling participants that the background music would affect performance in the memory task), they rated themselves equally assertive when coming up with six or twelve examples.
Schwarz further proves that cognitive ease becomes the true basis of the participants’ judgments: when the cognitive strain is explained by something else, it no longer becomes a factor of people’s ratings of their assertiveness.
Schwarz and his colleagues discovered that people who are personally involved in the judgment are more likely to consider the number of instances they retrieve and less likely to go by fluency. Students with no family history of heart disease were asked to recall three or eight behaviors that could affect their health. They felt safer if asked to retrieve many risky behaviors (which they found hard to do). Students with a family history of heart disease felt greater danger when they retrieved many instances of risky behavior.
This portion of the study perhaps implies that when people are personally involved in the judgment, they are more mentally invested in the answers that they provide, and thus they think more with System 2 (deliberation and logic) and less with System 1 (which, as in the previous example, relies purely on ease and intuition).
People are more affected by ease of retrieval than by content if they meet certain conditions, including the following: if they are engaged in another effortful task at the same time, if they are in a good mood, if they have a large amount of faith in intuition, or if they are made to feel powerful.
This last quality is particularly interesting, implying that if people are made to feel powerful, they have more confidence in their own intuition and judgment than they might otherwise feel.