Tuesday, April 6, 2010

How the blind can lead the blind indefinitely

Excerpt from the book The Science of Fear:

The confirmation bias

Once we have formed a view, we embrace information that supports that view while ignoring, rejecting, or harshly scrutinising information that casts doubt on it.Once a belief is established, our brains will seek to confirm it. Seeking to confirm our beliefs comes naturally, while it feels strange and counterintuitive to look for evidence that contradicts our beliefs.

In one of the earliest studies on confirmation bias, psychologist Peter Wason showed people a sequence of three numbers - 2,4,6 - and told them the sequence followed a certain rule. The participants were asked to figure out what that rule was. They could do so by writing down three more numbers and asking if they were in line with the rule. Once you think you've figured out the rule, the researchers instructed, say so and we will see if you're right.

It seems so obvious that the rule that the numbers are following is "even numbers increasing by two". So let's say you're taking the test. Obviously, your first step would be to ask: "What about 8,10,12? Does that follow the rule?" And you would be told, yes, that follows the rule. Now you are really suspicious. This is far too easy. So you decide to try another set of numbers. Does "14,16,18" follow the rule? It does.

At this point, you want to shout out the answer - the rule is even numbers increasing by two - but you know there's got to be a trick here. So you decide to ask about another three numbers - 20,22, 24. Right, again!

Most people who take the test follow exactly this pattern. Every time they guess, they are told they are right and so, it seems, the evidence that they are right piles up. Naturally, they become convinced that their initial belief is correct. Just look at all the evidence! And so they stop the test and announce that they have the answer: It is "even numbers increasing by two".

And they are told that they are wrong. That is not the rule. The correct rule is actually "any three numbers in ascending order".



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