Availability and category-frequency estimation

Abstract

Individuals judged how often examples of taxonomic categories had occurred in a study list. An availability hypothesis was tested-that frequency estimates are based on the retrieval of instances. Cued (by category names) recall of the examples served as an index of availability. The hypothesis was confirmed-there were strong positive correlations between frequency judgments and recall (with the influence ofactual frequency removed)-given one or more ofthe following conditions: List instances were not categorized aloud as they were presented; frequency estimation was preceded by cued recall; frequency estimation was delayed by a week. Limitations on availability occurred under other conditions-notably, when individuals, during list presentation, named the categories to which items belonged and received feedback about their categorizations. Under these circumstances, correlations of frequency estimation and recall were often not significantly different from zero, and frequency judgments and recall sometimes reacted differently to changes in independent variables (e.g., frequency judgments of young and elderly subjects did not differ reliably, even though cued recall ofyoung persons markedly exceeded that of elderly subjects).Tversky and Kahneman (1973) proposed that in judgments of the frequency with which members of a class have occurred, an availability heuristic may be usedthat is, frequency will be evaluated by the ease with which relevant instances come to mind. The experiments to be reported here were aimed at assessing the applicability of this hypothesis to the making of category-frequency judgments of episodic events. The task adopted was introduced by Alba, Chromiak, Hasher, and Attig (1980) and has since been used by others (e.g., Williams & Durso, 1986). In the present version, varying numbers of words were selected from common conceptual categories (e.g., animals and musical instruments) and shown to individuals in a random order. At the end of the list, names of the categories were presented, and the subjects were asked to estimate how many times words belonging to them had occurred in the study list.

The effect of category focus at encoding on category frequency estimation strategies

“…Indeed, the average within-subjects rank order correlation between objective category frequencies and estimated category frequencies was higher in the former than in the latter condition. This is consistent with the finding that encoding into a relevant category yields more accurate category frequency estimates than does encoding into an irrelevant category (see Hanson & Hirst, 1988) or not categorizing at all (Bruce et al, 1991; see also Barsalou & Ross, 1986;Freund & Hasher, 1989). An additional analysis revealed that the average rank order correlation between objective category frequencies and estimated category frequencies was higher for the participants who had relied on stored frequency information than for the participants who had relied on availability [Experiment 1A, M ϭ .77 vs. M ϭ .41, t(68) ϭ 5.65, p Ͻ .001; Experiment 1B, M ϭ .80 vs. M ϭ .57, t(66) ϭ 3.84, p Ͻ .001].…”

“…Still, people can use stored frequency information only if they have classified the instance into relevant categories. Whether they use availability despite the presence of stored category frequency information may depend on situation features, such as having engaged in recall prior to the estimation task (see, e.g., Betsch et al, 1999;Bruce et al, 1991) or being instructed to think carefully (e.g., Haberstroh & Betsch, 2002 911). In addition, people who have access to stored frequency information may base their estimates on that information but may supplement it with availability information.…”

“…However, some of them support this hypothesis only indirectly (e.g., Freund & Hasher, 1989;Hanson & Hirst, 1988). Others are difficult to interpret (Bruce et al, 1991) or were not designed to examine the present question (Conrad et al, 2003). Therefore, the aim of the present experiments was to examine how category activation at encoding determines how people estimate category frequencies.…”

“…However, the between-subjects correlations reported by Bruce et al (1991) confound within-subjects and betweensubjects variability (see Michela, 1990). Within each participant, recall and frequency estimate should be at least monotonically related if the participant uses the availability heuristic, even after controlling for objective frequency.…”

“…Manis et al (1993) even argued that it is the best operationalization. Therefore, estimating category frequencies through availability is supposed to create a strong correlation between the estimates and the number of instances recalled (e.g., Betsch et al, 1999;Bruce, Hockley, & Craik, 1991;Manis et al, 1993;Watkins & LeCompte, 1991). Moreover, the correlation should reflect a direct, rather than an indirect, relationship (e.g., Betsch et al, 1999;Bruce et al, 1991;Maley, Hunt, & Parr, 2000;Manis et al, 1993).…”