People often estimate probabilities based on how easy it is to think of examples.  Tons of examples pop into your head: High probability.  Zero examples come to mind despite brow-furrowing: Low probability.  This is known as the “availability heuristic.” 

I’ve been reading about availability for most of my career.  But as usual, Daniel Kahneman’s Thinking, Fast and Slow showed me I still have much to learn.  Neat:

A major advance in the understanding of the availability heuristic occurred in the early 1990s, when a group of German psychologists led by Norbert Schwarz raised an intriguing question: How will people’s impressions of the frequency of a category be affected by a requirement to list a specified number of instances? Imagine yourself a subject in that experiment:

First, list six instances in which you behaved assertively.

Next, evaluate how assertive you are.

Imagine that you had been asked for twelve instances of assertive behavior (a number most people find difficult). Would your view of your own assertiveness be different?

Schwarz and his colleagues observed that the task of listing instances may enhance the judgments of the trait by two different routes:

  • the number of instances retrieved
  • the ease with which they come to mind

The request to list twelve instances pits the two determinants against each other. On the one hand, you have just retrieved an impressive number of cases in which you were assertive. On the other hand, while the first three or four instances of your own assertiveness probably came easily to you, you almost certainly struggled to come up with the last few to complete a set of twelve; fluency was low. Which will count more–the amount retrieved or the ease and fluency of the retrieval?

The contest yielded a clear-cut winner: people who had just listed twelve instances rated themselves as less assertive than people who had listed only six. Furthermore, participants who had been asked to list twelve cases in which they had not behaved assertively ended up thinking of themselves as quite assertive! If you cannot easily come up with instances of meek behavior, you are likely to conclude that you are not meek at all.

Some applications?  Experiments find that people:

  • believe that they use their bicycles less often after recalling many rather than few instances
  • are less confident in a choice when they are asked to produce more arguments to support it
  • are less confident that an event was avoidable after listing more ways it could have been avoided
  • are less impressed by a car after listing many of its advantages

Maybe this is why Thinking, Fast and Slow has thirty eight chapters.  If you ask Kahneman for a dozen distinct examples of cognitive anomalies, he’s got it covered.