Availability Heuristic
The availability heuristic is judging how common or how large a category is by how easily instances of it come to mind. Nothing is counted. The speed with which examples arrive becomes the answer, and because the swap happens out of sight the estimate feels like a report about the world rather than a reading of your own memory. The originating paper is Amos Tversky and Daniel Kahneman's, in 1973, with Tversky as first author. The version of the heuristic most often quoted is the one the research has since moved past.
What it is
Tversky and Kahneman's 1973 paper introduced availability as one of a small set of heuristics people use in place of probability. The intuitive reading of it is about quantity: you recall more plane crashes than car crashes, so you overestimate how dangerous flying is.
The demonstration that changed what the heuristic is about is not theirs. It is Norbert Schwarz's. He asked people to list instances of their own assertive behaviour, some of them six instances and some of them twelve, and then to rate how assertive they were. If availability meant quantity retrieved, twelve should have produced higher self-ratings. It produced lower ones. Twelve is hard to generate. Six is easy. What people read off was not the size of the pile but the effort of building it.
Kahneman takes the result seriously enough to propose renaming the thing an unexplained unavailability heuristic, because the inference rests on retrieval feeling harder than it should have. The clinching evidence is that the effect can be switched off by giving the difficulty a false cause: tell people the background music is impairing recall and the struggle no longer counts as information about them.
In effect
Two things follow from the refinement, and both are awkward for the version that circulates.
The mechanism is fluency rather than frequency. Availability is a feeling-based judgement, closer to processing fluency and cognitive ease than to memory search. Any article treating it as remembering more plane crashes and therefore overestimating plane crashes is using the version that predates Schwarz.
And the effect is defeasible. An effect that a plausible external attribution can cancel is not a fixed property of the mind but a conditional inference. That is a more interesting finding and a considerably weaker one.
The concept is also unusually prone to arriving misnamed. Adrian Furnham's chapter on the mad genius prints the mechanism accurately, that films and popular books make the mad genius come readily to mind so people overestimate how often creativity and mental illness go together, and labels it the avoidant heuristic, attributing it to Dietrich in 2014. Tversky and Kahneman are named neither in the chapter nor in its bibliography, so a reader finishes with the right idea, the wrong name and no route back to the 1973 paper.
What it does not say
It does not say the effect is large or unconditional. Meta-analytic estimates are smaller and more conditional than confident popular presentations imply. This vault does not hold a specific meta-analysis for that, so it is recorded here as a caution rather than as a citation.
It does not say the heuristic has been overturned. Schwarz's result is a refinement. Something real is going on, and the basic effect is not among the failed items in this publication's audit of Thinking, Fast and Slow.
It does not come from the two-system framework. Kahneman notes that the framework did not exist when he and Tversky studied availability, so the system one and system two gloss applied to it later is retrofitted rather than original.
It is not quantified in the source this vault holds. The reversal studies are reported in Thinking, Fast and Slow with no sample size, no ratings, no effect size and no paper details for Schwarz beyond his name. A finding presented as decisive is presented unquantified, and it should be traced to Schwarz's primary paper before any of it is cited.
Sources
- Tversky, A., & Kahneman, D. (1973). "Availability: A Heuristic for Judging Frequency and Probability." Cognitive Psychology, 5. The originating paper. Tversky is first author, which is the correct credit even though Kahneman is the name attached to the idea in public.
- Schwarz, N. The ease-of-retrieval work. Named in Thinking, Fast and Slow; this vault holds no paper, year or journal for it, and none has been invented here.
- Kahneman, D. Thinking, Fast and Slow, ch. 12. This publication's audit of that book records that the body text is not a citable source and the endnotes are.
- Furnham, A. The New Psychology, ch. 33. Prints the mechanism under the name "the Avoidant Heuristic" and attributes it to Dietrich (2014). Recorded here as a specimen of a wrong label plus a missing originator.