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  • Writer's pictureDr Joanne Stuart

The basics of CBT: Confirmation bias.

CBT basics and confirmation bias

How do we develop beliefs and how could evolution be working against us?

What do you think it would be like if we were not able to predict anything about the world? What if we could not predict whether we would be attacked by the next human we met? Or predict where we might be able to get our next meal? This would be a scary world to live in.

So, beliefs are important because they make us feel the world is predictable and this makes us feel safe. If the world was unpredictable it would be highly anxiety provoking and very unpleasant.


Two children grow up in neighbouring houses: Tom and Pippa. The have very similar lives except Pippa’s parents believe that the only way their daughter will improve is by criticising her. Tom’s parents believe that positive reinforcements are the best form of parenting so they always praise their son when they think he has done well.

Does Pippa grow up feeling good or bad about herself?

Does Tom grow up feeling good or bad about himself?

Unfortunately the approach of Pippa’s parents has the undesired effect of the her feeling that she is not good enough. However, Tom has a positive sense of himself.

They go to the same school and both work hard and do equally well in their exams – achieving grades of above 85% for each paper. The parents of Pippa tell her that she has not done well enough and it just shows that she is a failure. The parents of Tom are complimentary of his efforts tell him that they are proud of him and the results.

What do you think Pippa will think of her future – good or bad, success or failure?

What about Tom?

It is likely, of course, that Pippa will believe that she is not good enough and will not do well. On the other hand, Tom may think the opposite.

Now remember, once we have developed a belief about something, we hold on strongly to it because if the world is not predictable then it is a scary place. So, we hold on to beliefs whether they are good or bad for us.

What we can see from the above example is that our beliefs develop because of our experiences. So how do we know our beliefs are true? Which child is right about themselves? Pippa or Tom?

Let us say that both children meet with their teacher. The teacher tells them both that they have done well and thinks that they will continue to do well in the future because they both work hard and have the aptitude for the subjects. Let us remember how important it is that we hold on to our beliefs, even if they are negative.

What do you think Pippa (with the negative self-esteem) is more likely to think – that her teacher is telling the truth, or that her teacher is just saying it to be nice?

What do you think Tom is more likely to think?

So, what we can understand from this is, depending on our experience, we find information in the environment that fits with our belief and we discard information that does not fit. If an individual thinks they are not good enough and ninety-nine compliments are paid to them they will find a way of dismissing them: “they didn’t mean it”; “they were mistaken”; “they were just being nice”; “they don’t really think that” and so on. However, if that person is criticised then they will believe that as the truth. Now, if a scientist looked at that data they would say that it was overwhelming evidence that the person was positive. This process is what us psychologists called ‘confirmation bias’. Although this process helps us to feel that the world is predictable and this makes us feel safe, at times this evolutionary mechanism has the unfortunate by-product of confirming negative self-beliefs when there is overwhelming evidence to the contrary.

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