Sophistry
No. 05 Cognitive bias

Availability Heuristic

Judge how common or risky something is by how easily an example comes to mind, not by the actual rate.

One case drawn very large in the foreground, beside a field of forty-eight identical small cases of which two are marked. a b
FIG. 5a, the case that comes to mind, drawn at the size it feels rather than the size it is. b, the field it is drawn from: forty-eight cases, of which the marked kind occurs twice.

Illustrative example

After seeing a shark attack story on the news, ocean swimming feels riskier than driving, when it's actually the opposite.

The availability heuristic estimates how common or risky something is based on how easily examples come to mind, rather than the actual rate. Vivid, recent, or heavily covered events come to mind easily and feel more common than they are.

News coverage makes this worse: rare, dramatic events get disproportionate airtime precisely because they’re rare and dramatic, which then makes them feel frequent.

When judging risk, look for the actual base rate rather than relying on how easily an example comes to mind.

Seen in the wild

Real, sourced instances of this technique in actual public debate.

Examples are chosen for how clearly they show the technique, not for who said it.

James Inhofe

Leans right

U.S. Senator (R-OK); Chairman of the Senate Environment and Public Works Committee

“In case we had forgotten because we keep hearing that 2014 has been the warmest year on record, I ask the chair: You know what this is? It's a snowball.”

February 26, 2015 (U.S. Senate floor)ABC News report quoting the floor remarks, corroborated by NBC News and CNN (opens on the source site)

WatchC-SPAN footage from the Senate floor (opens on the site hosting the footage)
Context
Inhofe carried a snowball onto the Senate floor and threw it, saying "this is today, this is reality." Weeks earlier NASA and NOAA had jointly announced that 2014 was the warmest year in the global surface temperature record.
Reading
The claim under dispute was a global annual average. The evidence offered was the weather outside one building on one afternoon. It persuades because it is right there in the room and everyone can see it, which is exactly the substitution the heuristic describes: the vivid example that comes to hand displaces the number it is supposed to be tested against. A cold day in Washington in February is not in tension with a record global mean, and there is no quantity of snowballs that would settle the question either way.

Know a good example?

Suggest a real, sourced instance of Availability Heuristic for this page. Submissions are reviewed before anything is added.

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