The availability heuristic, also known as availability bias, is a mental shortcut that relies on immediate examples that come to a given person's mind when evaluating a specific topic, concept, method, or decision. This heuristic, operating on the notion that, if something can be quickly recalled, it must be important, or at least more important than alternative solutions not as readily recalled, is inherently biased toward recently acquired information.
The mental availability of an action's consequences is positively related to those consequences' perceived magnitude. In other words, the easier it is to recall the consequences of something, the greater those consequences are often perceived to be. Most notably, people often rely on the content of their recall if its implications are not called into question by the difficulty they have in recalling it.
Overview and history
In the late 1960s and early 1970s, Amos Tversky and Daniel Kahneman began work on a series of papers examining "heuristic and biases" used in judgment under uncertainty. Prior to that, the predominant view in the field of human judgment was that humans are rational actors. Kahneman and Tversky explained that judgment under uncertainty often relies on a limited number of simplifying heuristics rather than extensive algorithmic processing. Soon, this idea spread beyond academic psychology, into law, medicine, and political science. This research questioned the descriptive adequacy of idealized models of judgment, and offered insights into the cognitive processes that explained human error without invoking motivated irrationality. One simplifying strategy people may rely on is the tendency to make a judgment about the frequency of an event based on how many similar instances are brought to mind. In 1973, Amos Tversky and Daniel Kahneman first studied this phenomenon and labeled it the "availability heuristic". An availability heuristic is a mental shortcut that relies on immediate examples that come to a given person's mind when evaluating a specific topic, concept, method, or decision. As follows, people tend to use a readily available fact to base their beliefs on a comparably distant concept. There has been much research done with this heuristic, but studies on the issue are still questionable with regard to the underlying process. Studies illustrate that manipulations intended to increase the subjective experience of ease of recall are also likely to affect the amount of recall. Furthermore, this makes it difficult to determine whether the obtained estimates of frequency, likelihood, or typicality are based on participants' phenomenal experiences or on a biased sample of recalled information.
However, some textbooks have chosen the latter interpretation introducing the availability heuristic as "one's judgments are always based on what comes to mind". For example, if a person is asked whether there are more words in the English language that start with a k or have k as the third letter, the person will probably be able to think of more words that begin with the letter k, concluding incorrectly that k is more frequent as the first letter than the third. In this Wikipedia article itself, for example, there are multiple instances of words such as "likely", "make", "take", "ask" and indeed "Wikipedia", but (aside from names) only a couple of initial K's: "know" and "key".
Research Chapman (1967) described a bias in the judgment of the frequency with which two events co-occur. This demonstration showed that the co-occurrence of paired stimuli resulted in participants overestimating the frequency of the pairings. To test this idea, participants were given information about several hypothetical mental patients. The data for each patient consisted of a clinical diagnosis and a drawing made by the patient. Later, participants estimated the frequency with which each diagnosis had been accompanied by various features of the drawing. The subjects vastly overestimated the frequency of this co-occurrence (such as suspiciousness and peculiar eyes). This effect was labeled the illusory correlation. Tversky and Kahneman suggested that availability provides a natural account for the illusory-correlation effect. The strength of the association between two events could provide the basis for the judgment of how frequently the two events co-occur. When the association is strong, it becomes more likely to conclude that the events have been paired frequently. Strong associations will be thought of as having occurred together frequently.
In Tversky & Kahneman's first examination of availability heuristics, subjects were asked, "If a random word is taken from an English text, is it more likely that the word starts with a K, or that K is the third letter?" They argue that English-speaking people would immediately think of many words that begin with the letter "K" (kangaroo, kitchen, kale), but that it would take a more concentrated effort to think of any words in which "K" is the third letter (acknowledge, ask). Results indicated that participants overestimated the number of words that began with the letter "K" and underestimated the number of words that had "K" as the third letter. Tversky and Kahneman concluded that people answer questions like these by comparing the availability of the two categories and assessing how easily they can recall these instances. In other words, it is easier to think of words that begin with "K", more than words with "K" as the third letter. Thus, people judge words beginning with a "K" to be a more common occurrence. In reality, however, a typical text contains twice as many words that have "K" as the third letter than "K" as the first letter.
In Tversky and Kahneman's seminal paper, they include findings from several other studies, which also show support for the availability heuristic. Apart from their findings in the "K" study, they also found: When participants were shown two visual structures and asked to pick the structure that had more paths, participants saw more paths in the structure that had more obvious available paths. In the structure that participants chose, there were more columns and shorter obvious paths, making it more available to them. When participants were asked to complete tasks involving estimation, they would often underestimate the end result. Participants were basing their final estimation on a quick first impression of the problem. Participants particularly struggled when the problems consisted of multiple steps. This occurred because participants were basing their estimation on an initial impression. Participants failed to account for the high rate of growth in the later steps due to the impression they formed in the initial steps. This was shown again in a task that asked participants to estimate the answer to a multiplication task, in which the numbers were presented as either 1x2x3x4x5x6x7x8 or 8x7x6x5x4x3x2x1. Participants who were presented the equation with the larger numbers first (8x7x6...), estimated a significantly higher result than participants with the lower numbers first (1x2x3...). Participants were given a short amount of time to make the estimation, thus participants based their estimates off of what was easily available, which in this case was the first few numbers in the sequence.
Explanations Many researchers have attempted to identify the psychological process which creates the availability heuristic.
Tversky and Kahneman argue that the number of examples recalled from memory is used to infer the frequency with which such instances occur. In an experiment to test this explanation, participants listened to lists of names containing either 19 famous women and 20 less famous men or 19 famous men and 20 less famous women. Subsequently, some participants were asked to recall as many names as possible whereas others were asked to estimate whether male or female names were more frequent on the list. The names of the famous celebrities were recalled more frequently compared to those of the less famous celebrities. The majority of the participants incorrectly judged that the gender associated with more famous names had been presented more often than the gender associated with less famous names. Tversky and Kahneman argue that although the availability heuristic is an effective strategy in many situations when judging probability, use of this heuristic can lead to predictable patterns of errors.
Schwarz and his colleagues, on the other hand, proposed the ease of retrieval explanation, wherein the ease with which examples come to mind, not the number of examples, is used to infer the frequency of a given class. In a study by Schwarz and colleagues to test their explanation, participants were asked to recall either six or twelve examples of their assertive or very unassertive behavior. Participants were later asked to rate their own assertiveness. Pretesting had indicated that although most participants were capable of generating twelve examples, this was a difficult task. The results indicated that participants rated themselves as more assertive after describing six examples of assertive compared with unassertive behavior, but rated themselves as less assertive after describing twelve examples of assertive compared with unassertive behavior. The study reflected that the extent to which recalled content impacted judgment was determined by the ease with which the content could be brought to mind (it was easier to recall 6 examples than 12), rather than the amount of content brought to mind.
Research by Vaughn (1999) looked at the effects of uncertainty on the use of the availability heuristic. College students were asked to list either three or eight different study methods they could use in order to get an A on their final exams. The researchers also manipulated the time during the semester they would ask the students to complete the questionnaire. Approximately half of the participants were asked for their study methods during the third week of classes, and the other half were asked on the last day of classes. Next, participants were asked to rate how likely they would be to get an A in their easiest and hardest classes. Participants were then asked to rank the difficulty they experienced in recalling the examples they had previously listed. The researchers hypothesized that students would use the availability heuristic, based on the number of study methods they listed, to predict their grade only when asked at the beginning of the semester and about their hardest final. Students were not expected to use the availability heuristic to predict their grades at the end of the semester or about their easiest final. The researchers predicted this use of the availability heuristic because participants would be uncertain about their performance throughout the semester. The results indicated that students used the availability heuristic, based on the ease of recall of the study methods they listed, to predict their performance when asked at the beginning of the semester and about their hardest final. If the student listed only three study methods, they predicted a higher grade at the end of the semester only on their hardest final. If students listed eight study methods, they had a harder time recalling the methods and thus predicted a lower final grade on their hardest final. The results were not seen in the easy final condition because the students were certain they would get an A, regardless of the study method. The results supported this hypothesis and gave evidence to the fact that levels of uncertainty affect the use of the availability heuristic.
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