CODEXCard 3 of 8 · Core Cognitive Biases
Availability heuristic
What comes to mind feels true.
The availability heuristic is a mental shortcut: when you need to estimate how likely or frequent something is, you check how quickly examples spring to mind. If they arrive fast, the thing feels common. If you struggle to think of any, it feels rare. Most of the time this works well enough, because frequent things usually are easier to remember.
The trouble is that memory is not a fair sample. Tversky and Kahneman described the heuristic in the early 1970s, and Kahneman returns to it often in Thinking, Fast and Slow. Dramatic events, recent stories and anything with strong emotion are stored more vividly, so they are retrieved more easily. Media coverage amplifies this, since unusual events are exactly what gets reported.
The limit to watch is how easily the effect can be turned on others. Feeding someone a few striking anecdotes and presenting them as evidence is a common persuasion trick. The honest defense, for yourself and others, is a simple question: does this feeling come from counting cases or from remembering stories?
Availability sits close to base rate neglect. Both replace the dull statistic with whatever is most memorable, and both are corrected by going looking for the actual numbers.
Example
After a friend tells you about a break-in on a nearby street, your neighbourhood suddenly feels unsafe, and you consider an expensive alarm system. The story is vivid and recent, so it dominates your estimate. Looking up local crime figures for the past few years might show that nothing has really changed.
Try it this week
When something strikes you as obviously common or rare this week, look up one real figure before you act on the feeling.
From Core Cognitive Biases (Daniel Kahneman · 2011).
