Editing Availability heuristic (section)

==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.<ref>{{Cite journal |last=Chapman |first=L.J |year=1967 |title=Illusory correlation in observational report |journal=Journal of Verbal Learning |volume=6 |pages=151–155 |doi=10.1016/s0022-5371(67)80066-5}}</ref> 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.<ref name="tversky">{{Cite journal |last1=Tversky |first1=Amos |last2=Kahneman |first2=Daniel |year=1973 |title=Availability: A heuristic for judging frequency and probability |journal=Cognitive Psychology |volume=5 |issue=2 |pages=207–232 |doi=10.1016/0010-0285(73)90033-9 |issn=0010-0285}}</ref>

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.<ref name="tversky" />

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.<ref name="tversky" />