According to Tversky and Kahneman's (1973, p. 208) availability heuristic, individuals estimate the frequency of an event or the likelihood of its occurrence “by the ease with which instances or associations come to mind.” Although this heuristic has stimulated an enormous amount of research (see Sherman & Corty, 1984; Taylor, 1982, for reviews), the classic studies on the issue are ambiguous with regard to the underlying process. For example, in one of the better known studies, Tversky and Kahneman (1973, Experiment 3) observed that participants overestimated the number of words that begin with the letter r, but underestimated the number of words that have r as the third letter. They presumably did so because words that begin with a certain letter can be brought to mind more easily than words that have a certain letter in the third position. Note, however, that this differential ease of recall may influence participants' frequency estimates in two different ways. On one hand, participants may use the subjective experience of ease or difficulty of recall as a basis of judgment, as suggested by Tversky and Kahneman's (1973) description of the availability heuristic. If so, they would estimate a higher frequency if the recall task is experienced as easy rather than difficult. On the other hand, they may recall as many words of each type as possible within the time allotted to them and may base their judgment on the recalled sample of words.