Oddly Wired
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reasoning

You judge how common a risk is by how easily you recall it.

The availability heuristic is a mental shortcut that relies on immediate examples that come to mind when evaluating a topic or decision.

If you can think of a vivid example of something—like a plane crash or a shark attack—you overestimate the probability of that event happening. The brain treats ease of recall as a proxy for frequency. If it is easy to imagine, your brain treats it as a high-probability event.

You mistake the vividness of a memory for the frequency of the event.

Where this comes from

Study
Tversky & Kahneman, 1973, Cognitive Psychology
What the check found
The definition is standard, and Tversky and Kahneman indeed published 'Availability: A heuristic for judging frequency and probability' in Cognitive Psychology in 1973.
Confidence
Well replicated

Related

One of these every day, and every one names the study it came from. When a finding is contested, it says so.