Availability Heuristic Mechanism
People judge frequency and probability based on the subjective ease of mentally retrieving examples rather than the content count of retrieved instances, using retrieval fluency as a proxy for actual frequency in the world.
Why This Is an Axiom
This identifies a specific computational mechanism—using metacognitive experience (ease) as a proxy for objective frequency—that represents a foundational heuristic in human judgment. The mechanism is distinct from simply "recalling examples"; it's the fluency of recall that drives estimates, explaining why single vivid examples can outweigh statistical base rates.
Key Evidence
Tversky and Kahneman's classic demonstrations show people overestimate frequencies of dramatic causes of death (terrorism, shark attacks) relative to mundane ones (diabetes, asthma) proportional to media coverage affecting retrieval ease, not to actual recall count. Schwarz's manipulation experiments show that when people are asked to generate many examples (making retrieval difficult), they actually lower frequency estimates despite retrieving more instances—proving ease, not count, drives judgment. Neuroimaging reveals that metacognitive fluency is processed in distinct regions from content retrieval.
Curriculum Connection
This axiom explains why the curriculum addresses base rate neglect, why single vivid examples bias judgment, and why statistical training must overcome intuitive frequency estimation. It justifies teaching students to distrust their ease-of-recall intuitions and substitute deliberate statistical reasoning. Understanding this mechanism explains common student errors (overweighting recent or vivid examples) and motivates interventions that make base rate information fluent (through visualization, repetition, or mnemonic devices) to compete with anecdotal ease.