Test your intuition: Can you tell a book by its cover?

Here’s a classic test of intuitive skills excepted from Daniel Kahneman’s Thinking Fast, Thinking Slow

As you consider this question, please assume that Steve – the subject — was selected at random from a representative sample.

Steve has been described by a neighbor as follows: “Steve is very shy and withdrawn, invariably helpful but with little interest in people or in the world of reality. A meek and tidy soul, he has a need for order and structure, and a passion for detail .”


* * * * *

Is Steve more likely to be a librarian or a farmer?


Intuitively, most people quickly conclude that Steve is a librarian.

According to Kahneman:

The resemblance of Steve’s personality to that of a stereotypical librarian strikes everyone immediately,

But, equally relevant statistical considerations are almost always ignored.

Did it occur to you that there are more than 20 male farmers for each male librarian in the United States?

Because there are so many more farmers, it is almost certain that more “meek and tidy” souls will be found on tractors than at library information desks.

However, we found that participants in our experiments ignored the relevant statistical facts and relied exclusively on resemblance … a simplifying heuristic (roughly, a rule of thumb) to make a difficult judgment. The reliance on the heuristic causes predictable biases (systematic errors) in their predictions.

In fact, there are several cognitive biases at work in this example …

First, is contextual bias.

I rigged the question – even more than Kahneman did – by showing you a picture of a meek guy “in context” – at his desk in front of some shelved books. Nobody said that was Steve!

Pictures are more powerful than words … and certainly – for most folks – more powerful than numbers. That’s called visual impact.

Once the picture was planted in your brain, it was pretty hard to even start thinking about farmers, right?

That’s called the anchoring effect.

Once people have a mental image of a male librarian, it’s tough for them to shake it.

Then comes the verbal description: meek, shy, structured, detail-oriented, etc.

Our intuition sub-consciously starts asking: what does that description most resemble?

Yep, a librarian.

That’s the resemblance bias.

Finally, there’s the dynamic called base rate neglect.

Kahneman says the most folks aren’t “statistically intuitive”.

One manifestation: They don’t ask themselves about the probability of something occurring given its frequency of occurrence in the relevant population.

They neglect the base rate … the simple fact that male farmers outnumber 20 to 1 makes it long odds that Steve is a librarian.

There you have it … one simple question and an array of cognitive biases: visual impact, contextual bias, anchoring, resemblance bias and base rate neglect.

Think of Steve the next time that you try to tell a book by its cover

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Source: Kahneman, Daniel,Thinking, Fast and Slow, 2011.

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One Response to “Test your intuition: Can you tell a book by its cover?”

  1. John Carpenter Says:

    Ha! Tricking us with a picture. I think “not being suspicious of source info” has to work into the decision bias issue here. Gotta admit though, even knowing the stats I cannot shake the librarian thing.

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