Cognitive Heuristics - Review of Tversky Kahneman's Availability Heuristic

Cogito, ergo sum

(Descartes, Discourse on Method, 1637)

The endeavour to understand human reason is perhaps one of the oldest pursuits known to man and indeed many have described this desire as being at the core of what makes us human. Although this area was originally the playing field of philosophers - such as Aristotle, Hobbes, Descartes, Hume and Kant, to name but a few - their insights laid the foundation for the transition of the field to the more scientific endeavour of cognitive psychology. Traditional theories may have focussed on more normative aspects of directed thinking, intended to identify practical strategies through logic and systematic argument, however modern cognitive theories attempt to understand the underlying psychological processes of thought and its dynamic effects on our judgment and behaviour (Sternberg, 2005).

When faced with judgment in a problem-solving situation, the human brain relies on a multitude of complex strategies. The most influential work in problem-solving cognition was perhaps that of the Gestalt psychologists in the early twentieth century (King et. al, 1994). Researchers such as Wertheimer, Duncker and Luchins published compelling research about the structure and dynamics of problem-solving strategies, forming the basis for recent theories such as Piaget's Cognitive Development and Bandura's Social Cognitive Theory (King et. al, 1994). Modern pioneers call for a multi-faceted approach to understanding cognition, eager to merge known cognitive processes (e.g. deductive/inductive inference, symbolic and analogical representation, abstract reasoning, algorithmic logic and pattern detection) into one unified theory (e.g. Newell, 1990).

Whilst it may be easier to make good judgments if privy to all pertinent information or given hours for directed research, many of the decisions we make in every-day life are made bereft of such advantages. When faced with a knowledge-poor situation or under constraints of time or uncertainty, we instead depend on 'rules of thumb' or cognitive heuristics (Gleitman et. al, 2004; Tversky & Kahneman, 1983). In a series of papers in the 1970's, Amos Tversky and Daniel Kahneman 'reshaped the psychology of human judgment' by proposing that instead of dependency on complex systems, we in fact only use a limited number of simple cognitive heuristics when presented with limited 'outside' information (Hollyoak & Morrison, 2005). For instance, they suggested that people judge likelihood of events based on how it 'represents' a larger group or other similar examples - a phenomena they coined the representativeness heuristic (Tversky & Kahnmeman, 1972). As well as being backed by a wealth of empirical research (Sherman & Corty, 1984 for review), this idea fits well with accepted models of learning theory, namely that we tend to categorise things in the memory and store things by association (Sternberg, 2006) and are prone to effects such as stereotyping (Gleitman et. al, 2004)

Another heuristic demonstrated by Tversky and Kahneman is the availability heuristic (Tversky & Kahneman, 1973). This heuristic is based on the idea that when asked to judge frequency or probability of an event, we base our judgement on how easy it is to think of relevant examples. In an experiment to test this heuristic they presented participants with four lists of names: two lists containing 19 famous women and 20 less famous men, and two lists containing 19 famous men and 20 less famous women (Study 8, 1973). Using a between-groups design, the first group were asked to recall as many names as possible and the second group were asked to estimate which class was more frequent, either famous or less famous. The results gave two insights. Firstly, that the famous names were most easily recalled compared to the less famous names. Moreover, despite the fact that the less famous names were more frequent, the majority of the participants mistakenly judged that the famous names appeared more often. Therefore a key factor that emerged from this study (and others) is that whilst the availability heuristic serves as an effective strategy in many situations - that is to say, they lead to accurate judgements - they can also lead to 'systematic errors', particularly when judging frequency (Tversky & Kahneman 1973,1974).

The idea that this simple heuristic forms the basis of frequency judgements and lead to bias is a significant one in judgement research. According to the Social Science Citation Index(Institute for Scientific Information, 1970-1982), Tversky & Kahneman's 1973 paper on the availability heuristic is cited 24 times per year compared to an average of 1.4 times per year (Armstrong, 1984). However, despite these impressive figures their original research has received some criticism (Schwarz et al, 1991; Taylor et al, 1982; Gigerenzer et. al, 1991). Some researchers have expressed concern about conflated variables, suggesting that the design of their earlier experiments was ambiguous in determining how the availability heuristic actually works. For example, consider again the experiment described above. Do the subjects base their frequency estimates on the subjective ease of recalling famous names or do they base their estimates on the actual amount of content recalled?

In 1991, Schwarz et. al conducted experiments intended to address this 'problem'. They set recall tasks to report either 6 or 12 assertive behaviours that participants had previously been involved in; 6 instances being assumed (based on pre-testing) as 'easy' to recall and 12 instances as 'difficult'. They then asked participants to judge their own assertiveness. The results showed that despite being able to recall 12 assertive behaviours they had personally engaged in, this higher amount of recall didn't affect their perception of their own assertiveness. In fact, because the task of trying to recall 12 behaviours was subjectively viewed as more difficult, they judged their own assertiveness to be less than average. These findings seemed to address this confusion about the underlying process and supports Tversky and Kahnemans original assertion (1973) that frequency judgments are based on the subjective ease of recall.

Other researchers have questioned other factors concerning the validity of their experimental design. Firstly, replication of the original studies was non-existent up to as recently as 1998 (except for one paper in 1991 by White) and moreover, their findings of bias in frequency judgment seems to contradict current research that indicates 'humans are able to derive answers that reflect the actual relative frequencies of the events with great fidelity' (Watkins & LeCompte,1991; Jonide & Jones, 1992; Sedlmeier et al, 1998).

This is a concern that is mirrored by researchers such as Gerd Gigerenzer (1991;1996), who have engaged in a lively debate over this topic and other criticisms such as proposed subtleties of difference of meaning between probability and frequency. Future research should be focussing on these criticisms with an attempt to iron out any difficulties. Some recent research by Brown et al (1995) on exemplar pairs have provided some evidence that the availability heuristic is only one of many strategies involved in frequency judgment. Indeed, recent work on support theory by Tversky and Rottenstreich (1997) suggests that saliency and explicity of description of events can have a significant influence on how one judges their frequency or probability and this idea is backed up by several more recent studies (Sternberg, 2006). Therefore, perhaps a more integrated approach to future research is required, working towards something like a Unified Theory like that proposed by Newell - certainly the complexity of the human mind would indicate we are only scratching the surface.


Armstrong, J. (1984) Review of Daniel Kahnemann, Paul Slovic, and Amos Tversky (eds.), Judgment Under Uncertainty: Heuristics and Biases, Science, 185 (4157).

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Newell, A. (1990). Unified Theories of Cognition. Harvard University Press. Cambridge, Massachusetts.

Schwarz, N., Bless, H., Strack, F. & Klumpp, G. (1991) Ease of Retrieval as Information: Another Look at the Availability Heuristic, Journal of Personality and Social Psychology, 61(2), 195-202.

Sedlmeier, P., Hertwig, R. & Gigerenzer, G. (1995) Are Judgments of the Positional Frequencies of Letters Systematically Biased Due to Availability? Journal of Experimental Psychology: Learning, Memory, and Cognition, 24 (3), 754-770

Sherman, S. J., & Corty, E. (1984). Cognitive heuristics. In R. S. Wyer & T. K. Sruli (Eds.), Handbook of Social Cognition (Vol. 1, pp. 189-286). Hillsdale, NJ: Eribaum.

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