Bryan Caplan  

Give Me A Dozen Examples

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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.


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COMMENTS (4 to date)
Chris Koresko writes:

If I understand you and Kahneman correctly, the hypothesis is that someone who tries to list a dozen instances of his assertiveness finds that difficult, and the difficulty leads him to question whether he is in fact assertive. But when asked to name only six instances, the relative ease of doing so leads him to think himself assertive. It's the ease of coming up with examples that matters, according to this hypothesis.

I offer an alternative hypothesis: Asking someone to list a given number of instances creates an impression that a standard has been set. Someone who fails to easily come up with enough examples to meet that standard considers himself a poor example, while someone who meets the implicit standard easily considers himself an exemplar.

So if you ask me to name six times I was assertive, and I do that easily, then I think I must be assertive, because implicitly the test for assertiveness is the ability to name six times I was assertive.

Brian Moore writes:

I agree with Chris' interpretation -- I don't think it contradicts what Kahneman was trying to say (not sure if Chris was implying that) -- but I definitely think that the "standard setting from the authority figure" factor is what's happening here.

Doctors use a similar trick when trying to get alcohol usage data from potentially over-drinking patients. Instead of asking "how much do you drink?" which causes the patient to low-ball, or "do you drink more than X?" where X is a value that the doctor considers reasonable (and the patient will hear that tone in their voice, and again low-ball), they are instructed (at least at my wife's med school) to say "do you drink more than Y?" where Y is a ridiculously high amount.

The patient, relieved that they aren't some kind of crazy alcoholic, will say "oh no no, nothing like that, I only have 10 beers a night!"

Ken B writes:

Ever since I learned about the availability heuristic I see it everywhere.

Carl C writes:

@Chris Koresko
I think your alternative hypothesis is very plausible.

In your story, I consciously assume that the number I am given is a standard. In Kahneman's story, I don't evaluate it consciously, but act as if the number is the standard. Outside of the lab, I am not given a standard at all, and must select one for myself. This third alternative adds an even greater degree of error to my conclusions.

But, the practical consequence of all three alternatives are the same: In the absence of an objective standard, this heuristic will lead to inaccurate conclusions.

Also, the lesson from both hypotheses are the same: This heuristic should be reserved for cases where there are objective standards and where instances can be counted accurately.

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