The Availability Error is a Trap for Our Thinking

If you are driving and pass an accident on the road you will probably slow down and drive more safely for a while. A similar thing happens if you pass a police car. When people hear about a burglary they are more inclined to lock their doors and windows. When they hear about a lottery win they are more likely to buy a ticket.

When asked to rate the probability of different causes of death people tend to rate more "newsworthy" events as more likely. People often rate the chance of death by plane crash higher after they have heard about a plane crash. The likelihood of natural disaster is overestimated because these events are more reported than more common causes of death.

We are heavily influenced by what we have heard or seen recently. We therefore place more value on the information that is immediately available. This leads to the availability error. In his book, Irrationality, Stuart Sutherland gives the example of a psychology experiment in which people first had to learn a short list of words. Some of the people learnt the words adventurous, self-confident, independent and persistent. A second group learnt the words reckless, conceited, aloof and stubborn. In a separate second task they were told to read a story. They all read the same story about a young man who had some dangerous hobbies, thought highly of his abilities, had few friends and rarely changed his mind once it was made up. They were then asked to describe the man. It was made very clear to all the people that learning the initial list of words had nothing to do with the second task concerning the story. However, those people who had learnt the first list of words gave a much more favourable description of the young man than those who had learnt the second list. The recently learnt words significantly affected how the people judged the man in an unconnected situation.

What we see first tends to influence us most. This was proved in an experiment in which some people were asked to quickly estimate the product of:

1 x 2 x 3 x 4 x 5 x 6 x 7 x 8

A second group of people was asked to quickly estimate the product of:

8 x 7 x 6 x 5 x 4 x 3 x 2 x 1

(Take a quick guess at what you think the answer is). The interesting result was that people in the first group consistently estimated a lower total than people in the second group. The average of the estimates of the first group was 512 and in the second group it was 2250 - a big difference. People who see the small numbers first are influenced by those numbers to estimate a lower total than people who see large numbers first. The first numbers they see have a disproportionate impact. Incidentally both groups severely underestimated the correct answer, which is 40,320. What did you guess?

A common example of the availability error is when we use a memorable but unlikely piece of evidence rather than take a more balanced view. Someone might say, 'I don't think smoking is that bad because my Uncle Arthur smoked 20 cigarettes a day and he lived till he was 92.' The story of Uncle Arthur is available and memorable but highly unrepresentative of smokers as a whole. Similarly you hear people say things like, 'Italians love gambling. I have known three Italians who were all heavy gamblers.' This person's opinion is heavily over influenced by the three characters he remembers rather than the thousands of Italians who do not gamble.

Paul Sloane speaks on lateral thinking and innovation. He is the author of How to be a Brilliant Thinker.