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Definition

The availability heuristic is a mental shortcut that uses the ease with which examples come to mind to make judgements about the probability of events. The availability heuristic operates on the notion that if you can think of it, it must be important. The availability of consequences associated with an act is positively related to perceptions of the magnitude of consequences of that act.Sometimes, this heuristic is beneficial, but the frequency that events come to mind are usually not accurate reflections of their actual probability in reality.

Overview and History

When faced with the difficult task of judging probability or frequency, people use a limited number of strategies, called heuristics, to simplify these judgments. One of these strategies, the availability heuristic, is our tendency to make a judgement about the frequency of an event based on how easy it is to recall similar instances. In 1973, Tversky and Kahneman first studied this phenomenon and labeled it the Availability Heuristic. The availability heuristic an unconscious process that operates on the notion that "if you can think of it, it must be important." The availability of consequences associated with an act is positively related to perceptions of the magnitude of consequences of that act. In other words, how readily an example can be called to mind is related to perceptions about how often this event occurs. People tend to use a more reachable attribute to base their beliefs about a relatively distant attribute. In addition, the availability of others who believe that a particular act is morally acceptable is positively related to others' perceptions of the morality of that act.

Media

Media coverage can help fuel a person's example bias with widespread and extensive coverage of unusual events, such as homicide or airline accidents, and less coverage of more routine, less sensational events, such as common diseases or car accidents. For example, when asked to rate the probability of a variety of causes of death, people tend to rate more "newsworthy" events as more likely because they can more readily recall an example from memory. For example, in the USA, people rate the chance of death by homicide higher than the chance of death by stomach cancer, even though death by stomach cancer is five times higher than death by homicide. Moreover, unusual and vivid events like homicides, shark attacks, or lightning are more often reported in mass media than common and unsensational causes of death like common diseases. Another instance of biased ratings is the relative overestimation of plane crash deaths, compared to car-accident deaths.

Research

• In a well known availability heuristic study, participants were asked to describe either 6 or 12 examples of assertive, or unassertive, behavior. Participants were later asked to rate their own assertiveness. The results showed that participants rated themselves as more assertive after describing 6, rather than 12, examples for the assertive behavior condition, and conversely rated themselves as less assertive after describing 6, rather than 12, examples for the unassertive behavior condition. The study reflected that the recalled content was qualified by the ease with which the content could be brought to mind (it was easier to recall 6 examples than 12)

• In another well-known study, 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?” Results showed that participants overestimated the number of words that began with the letter “k”, but underestimated the number of words that had “k” as the third letter. Researchers believed that people answer questions like this by comparing the availability of the two categories by assessing how easily they can recall these instances. In other words, it is easier to think of words that begin with K, than words with K as the third letter, so people judge words beginning with a K to be a more common occurrence. The truth is, a typical text contains twice as many words that have K as the third letter than K as the first letter.

• Chapman (1967) described a bias in the judgment of the frequency with which two events co-occur. Their 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 associates will be thought of as having occurred together frequently.

Applications

Health

A previous research study examined the impact of the availability heuristic in the perceptions of health-related events: lifetime risk of breast cancer, subjective life expectancy, and subjective age of onset of menopause. In each section, three conditions were set up: control, anchoring heuristic, and availability heuristic. The findings revealed that availability and anchoring were being used to estimate personal health-related events. Availability also impacted perceived health risks.

In another study, risk assessments of contracting breast cancer were based on experiences with an abnormal breast symptom, experiences with affected family members and friends, beliefs about living a healthy lifestyle, and trust in health providers.

Participants in a 1992 study read case descriptions of hypothetical patients who varied on their sex and sexual preference. These hypothetical patients showed symptoms of two different diseases. Participants were instructed to indicate which disease they thought the patient had and then they rated patient responsibility and interactional desirability. Consistent with the availability heuristic, either the more common (influenza) or the more publicized (AIDS) disease was chosen.

Business and Economy

A previous study sought out to analyze the role of the availability heuristic in financial markets. Researchers defined and tested two aspects of the availability heuristic

1. Outcome Availability - availability of positive and negative investment outcomes
2. Risk Availability - availability of financial risk

Researchers tested the availability effect on investors' reactions to analyst recommendation revisions and found that positive stock price reactions to recommendation upgrades are stronger when accompanied by positive stock market index returns. On the other hand, negative stock price reactions to recommendation downgrades are stronger when accompanied by negative stock market index returns. On days of substantial stock market moves, abnormal stock price reactions to upgrades are weaker, and abnormal stock price reactions to downgrades are stronger. These availability effects are still significant even after controlling for event-specific and company-specific factors.

Criminal Justice

The media usually focuses on violent or extreme cases, which are more readily available in the public's mind. This may come into play when it is time for the judicial to evaluate and determine the proper punishment for a crime. In a previous study, respondents rated how much they agreed with hypothetical laws and policies such as "Would you support a law that required all offenders convicted of unarmed muggings to serve a minimum prison term of two years?" Participants then read cases and rated each case on several questions about punishment. As hypothesized, respondents recalled more easily from long-term memory stories that contain severe harm, which seemed to influence their sentencing choices to make them push for harsher punishments. This can be eliminated by adding high concrete or high contextually distinct details into the crime stories about less severe injuries.

A similar asked jurors and college students to choose sentences on four severe criminal cases in which prison was a possible but not inevitable sentencing outcome. The sentences given by students were equal to or less severe than those given by judges. Researchers explain this with the availability heuristic because people attempt to recall prior cases and are influenced by the severity of the offenses. Studies like this expose insidious biases in the courtroom.

Examples

• After seeing news stories about child abductions, people may judge that the likelihood of this event is greater.

• Many people think that the likelihood of dying from shark attacks is greater than that of dying from being hit by falling airplane parts, when more people actually die from falling airplane parts. When a shark attack occurs, the deaths are widely reported in the media whereas deaths as a result of being hit by falling airplane parts are rarely reported in the media.

• A person argues that cigarette smoking is not unhealthy because his grandfather smoked three packs of cigarettes a day and lived to be 100. The grandfather's health could simply be an unusual case that does not speak to the health of smokers in general.

• A politician says that walnut farmers need a special farm subsidy. He points to a farmer standing nearby and explains how that farmer will benefit. Others who watch and discuss later agree that the subsidy is needed based on the benefit to that farmer. The farmer, however, might be the only person who will benefit from the subsidy. Walnut farmers in general may not necessarily need this subsidy.

• A person claims to a group of friends that drivers of red cars get more speeding tickets. The group agrees with the statement because a member of the group, "Jim," drives a red car and frequently gets speeding tickets. The reality could be that Jim just drives fast and would get a speeding ticket regardless of the color of car that he drove. Even if statistics show fewer speeding tickets were given to red cars than to other colors of cars, Jim is an available example which makes the statement seem more plausible.

• Someone is asked to estimate the proportion of words that begin with the letter "R" or "K" versus those words that have the letter "R" or "K" in the third position. Most English-speaking people could immediately think of many words that begin with the letters "R" (roar, rusty, ribald) or "K" (kangaroo, kitchen, kale), but it would take a more concentrated effort to think of any words where "R" or "K" is the third letter (street, care, borrow, acknowledge); the immediate answer would probably be that words that begin with "R" or "K" are more common. The reality is that words that have the letter "R" or "K" in the third position are more common. In fact, there are three times as many words that have the letter "K" in the third position, as have it in the first position.

• Where an anecdote ("I know a Brazilian man who...") is used to "prove" an entire proposition or to support a bias, the availability heuristic is in play. In these instances the ease of imagining an example or the vividness and emotional impact of that example becomes more credible than actual statistical probability. Because an example is easily brought to mind or mentally "available," the single example is considered as representative of the whole rather than as just a single example in a range of data.

• A person sees several news stories of cats leaping out of tall trees and surviving, so he believes that cats must be robust to long falls. However, these kinds of news reports are far more common than reports where a cat falls out of the tree and dies, which may in fact be a more common event.

Critiques

• Some researchers have suggested that perceived causes or reasons for an event, rather than imagery of the event itself, influence probability estimates. Evidence for this notion stems from a study where participants either imagined the winner of the debate, or came up with reasons for why Reagan or Mondale would win the debate. The results of this study explained that imagining Reagan or Mondale winning the debate had no effect on predictions of who would win the debate. However, imagining and considering reasons for why Reagan or Mondale would win the debate did significantly affect predictions.

• Other psychologists argue that the classic studies on the availability heuristc are vague and do not explain the underlying processes. For example, in the famous Tversky and Kahnmenn study, Wanke et al. believe that this differential ease of recall, may alter subjects’ frequency estimates in two different ways. In one way, as the availability heuristic suggests, the subjects may use the subjective experience of ease of difficulty of recall as a basis of judgment. Wanke et al. assert that if this is done, they would predict a higher frequency if the recall task is experienced as easy rather than difficult. In a contrasting scenario, Wanke et al. suggest that the subjects may recall as many words of each type as possible within the time given to them and may base their judgment on the recalled sample of words. If it is easier to recall words which begin with a certain letter, these words would be over-represented in the recalled sample, again producing a prediction of higher frequency. It must be noted, however, that in the second scenario the estimate would be based on recalled content rather than on the subjective experience of ease of recall.

See also

• Affect heuristic
• Anecdotal evidence
• Anecdotal value
• Attribute substitution
• Gambler's fallacy
• Misleading vividness
• Processing fluency
• Representativeness heuristic
• Texas sharpshooter fallacy
• Agenda-setting theory
• List of cognitive biases