What do people do when they want to estimate the frequency of certain categories (for example the divorce rate among professors, poisonous snakes)? The reliance on the ease of memory search (instances coming to mind) is called the ‘availability heuristic’. This heuristic is both an automatic operation (System 1) as a deliberate problem-solving strategy (System 2).

The availability heuristic substitutes questions, which results into biases (systematic errors).  Examples of factors that are potential sources of bias are:

• Conspicuous events attract attention and are easy to retrieve from memory. Instances of divorces among famous actors will come easily to mind, making you prone to exaggerate the frequency of divorces among famous actors.

• Dramatic events temporarily increase the availability of the concerning category. Hearing about a fatal accident with a bike on the news temporarily influences your opinion about the safety of bikes.

• A personal experience is more available than an incident that happened to someone else. Pictures are more available than words and vivid examples are more available than statistics.

It requires a fair amount of effort to resist so many potential availability biases. It takes reconsidering our intuitions and impressions by asking yourself questions. Examples are “Is my impression that house robbery is a major national problem due to my neighbor’s houses recently being robbed?” or “Is it possible that I feel no need to eat healthy because none of my friends got sick last year?”

A well-known study of availability indicates that being aware of our own biases contributes to peaceful marriage, and potentially other joint projects. Surveys among spouses about their own contributions to housekeeping and causing arguments demonstrated that they remember their own contributions more clearly. The same goes for people working in group projects: most members feel they had put in more effort than others.

An experiment carried out by psychologist Schwarz helped us gain a better understanding of the availability heuristic. He wanted to assess how our impressions of the frequency of a category will be influenced by the task to list a certain number of instances. The experiment showed that the listing instances task enhances the judgment by the ease with which they come to mind and the number of instances retrieved. The first instances will come easily to mind, but the fluency of the last instances will be low. People who list eight instances of indecisive behavior will rate themselves as less indecisive than people who list only three. People who are asked to list eight instances of decisive behavior will think of themselves as rather indecisive. Self-rating is dominated by the ease with which instances come to mind. The fluency of the retrieval counts more than the amount of retrieved instances. Numerous experiments have yielded paradoxical results. Other examples are: people who are asked to report more arguments to support a choice are less confident in that choice, people who had to list many advantages of a gadget were afterwards less impressed by it and students who listed more ways to improve a course rated it better. 

Results are not always paradoxical, sometimes content trumps the ease of retrieval. You understand a pattern of behavior if you know how to reverse it. Under which conditions will reversal take place? During the task, the ease with which instances of behavior come to mind changes. The first instances come to mind easily, then it gets harder. A gradual drop in the fluency of the retrieval will be expected, but the drop between the low number and the high number of instances will be greater than expected. You tend to think: ‘if it is so much harder than expected to come up with more instances of modesty, then I’m probably not very modest’. This assumption rests on a surprise (a worse than expected fluency). The availability heuristic turns into an ‘unexplained unavailability’ heuristic. This heuristic can be disrupted by providing an explanation for the diminished fluency of retrieval, like background music, a background color, curved text boxes or other irrelevant factors. By eliminating the surprise, the low fluency stops influencing the judgement.

System 1 sets expectations and generates surprise in case of violated expectations. System 1 also retrieves potential causes of the surprise, normally by finding one among recent surprises. System 2 is capable of resetting the expectations of System 2, making an normally surprising event appear normal. The ease with which instances are retrieved is a System 1 heuristic, which gets replaced by a focus on content as soon as System 2 becomes more engaged. Someone that lets System 1 guide him/her is more susceptible to availability biases than some someone who is more vigilant. Conditions in which someone is more affected by the ease of retrieval than by the retrieved content:

• Scoring low on a depression scale

• Being in a good mood

• Being simultaneously engaged in another demanding task

• Being or feeling powerful