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.  [8]

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.  [4]

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.  [9]