Confirmation bias is a cognitive error that causes people to interpret and process information in a way that confirms their existing beliefs and assumptions rather than disconfirming them. This means that people tend to select and interpret information and evidence that confirms their own beliefs and biases, while ignoring or rejecting information that contradicts them. Confirmation bias can lead people to make biased decisions and experience a distortion in their perception and thinking.

For example, the confirmation bias can occur in the judgement of political decisions or in the evaluation of products and services. If a person already has a particular political belief, they may tend to accept only information and arguments that confirm these beliefs, ignoring information and arguments that contradict them. Similarly, a person may tend to accept only reviews and testimonials that confirm their pre-existing opinions and prejudices, while rejecting or ignoring reviews and testimonials that contradict them.