The availability heuristic is a mental shortcut people routinely use to estimate how common or likely something is: rather than consulting actual statistics, people tend to judge an event's probability by how easily examples of it come to mind. This shortcut works reasonably well in many everyday situations, since genuinely common events do tend to come to mind more easily than rare ones — but it systematically breaks down whenever how memorable or easily recalled something is comes apart from how statistically frequent it actually is, which happens more often than people generally assume.
Ease of recall is a genuine but imperfect proxy for real frequency
Using ease of recall as a stand-in for actual statistical frequency is a reasonable strategy precisely because, across many ordinary situations, the two genuinely do track each other fairly well — events that happen often are, on average, also events a person has encountered often enough to recall relatively easily. The heuristic becomes systematically misleading, though, whenever some factor other than genuine statistical frequency also makes an event easier to recall — vividness, emotional intensity, or simply how recently a person happened to encounter or hear about it — since the availability heuristic doesn't actually distinguish between an event that's easy to recall because it's genuinely common and an event that's easy to recall for some unrelated reason entirely.
Media coverage and vivid personal experience distort availability without changing real frequency
Media coverage is one of the clearest and most consistently studied sources of this kind of distortion: dramatic, unusual events, precisely because they're unusual, tend to receive disproportionate media coverage relative to how common they actually are, which in turn makes them easier to recall and therefore feel considerably more statistically probable than routine events that occur far more often but attract comparatively little media attention. A single vivid personal experience can distort a person's own sense of a given risk's likelihood in the same basic way, making that specific risk feel more probable going forward simply because it's now easy for that person to recall a specific memorable instance of it, even though one memorable personal experience says very little, on its own, about the risk's actual underlying statistical frequency.
What we're still unsure about
The availability heuristic itself, and its well-documented tendency to distort probability judgements when memorability and actual frequency diverge, are extensively confirmed across decades of cognitive psychology research. What remains more genuinely an active area of ongoing research is exactly how effectively people can be trained or prompted to correct for the availability heuristic's biasing effect in a specific real decision, once they're aware of it in principle — some interventions show modest genuine improvement in probability judgements once people are explicitly prompted to consider actual statistics rather than relying on ease of recall alone, but researchers continue studying how durable and how broadly transferable that kind of improvement actually is across different kinds of judgements and contexts, rather than there being one universally reliable debiasing technique.
This sits inside Cognitive Biases & Heuristics, one of seven topics in Cognitive Psychology, one of four domains in Psychology, one of seventeen subjects the app can quiz you on.