Confirmation Bias

Hi everyone, this week’s post is an expansion of a brain teaser that I wrote a few months ago about whether we are innately logical – to read that and see how you get on in a test of logic check here. In this, I explained that we tend to fail at classic logic tests because we look for information that supports what we already know, rather than taking all available information into consideration to make our judgments – this is called confirmation bias. It operates in 2 ways: by selective searching for information, and biased interpretation of information.

Once you think about it, it’s surprisingly common in everyday situations. People have superstitions because they notice a link between a certain action and a result, so every they will continue to carry out that action. They do this even if it doesn’t always work – these instances are ignored, but every time the superstition ‘works’ it sticks in their memory and reinforces their actions.

Although this is a relatively simple example, the way we use reasoning has important implications, for example in the criminal justice system. Members of the jury must consider all the information presented to them in order to come up with the correct decision. However, several psychological studies have shown that people’s judgments are easily affected by prejudice and personal expectations, or by a piece of evidence which seems to fit.

For example, Ask & Granhag (2005) asked both criminal investigators and students to read facts about a murder case, but manipulated information so that half of the participants had background information suggesting that a prime suspect had a motive, while the other half were told there might be someone else involved. They found that the students thought it was more likely to be the prime suspect, but only when they had a motive. The investigators showed a similar effect and were less likely to consider problems with the evidence when a prime suspect was identified, rather than if there was someone else – but importantly only if they had a ‘need for cognitive closure’ (basically time pressure and emotional investment in the decision). This shows the imprecise nature of our decision making and how our emotions and initial thoughts can easily cloud our judgments.

In order to avoid confirmation bias, it is important to take into account any information which goes against what you originally thought. In science, people need to actively look for information to go against their theory, because when you’ve disproved alternatives you can be sure that your theory is correct. So it might be worth keeping this in mind..

confirmation bias


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