From The Propaganda Professor:
You’ve no doubt seen it more times than you can count: a friend or relative shares something on social media that is manifestly erroneous, to the point of being self-parody. Yet it’s something that this person, and many others, passionately and unquestioningly believe to be accurate and valid. They have passed it on because they saw someone else pass it on, and it resonated with their beliefs, so they shared it without bothering to do one second of research about it. They, in short, have exhibited blatant confirmation bias — which, as the name suggests, is a bias toward confirming the validity of your biases.
Actually confirmation bias consists of three biases in one. First there’s selection bias, which causes you to focus only (or mostly) on information and narratives that support your beliefs. If you believe, for instance, that undocumented (“illegal”) immigrants pose a threat to your safety, then you might zero in on news stories about the instances of such individuals committing crimes — and ignore (or deny) statistics showing that they actually commit fewer crimes than U.S. citizens.
Then there’s interpretation bias. Not only do you selectively seek out facts, you selectively interpret the facts you find. Continuing with the anti-immigrant example, you’d attribute the criminal behavior of the individuals in question to their being undocumented immigrants, rather than considering other factors that are probably much more important. If the criminal is a murderer, for instance, it would be much more logical (if also absurd) to focus on the fact that he is male, since males commit by far the greater share of violent crimes, and thus gender is certainly a much more significant factor than immigration status.
Finally there’s memory bias, which prompts you to be selective and even creative in what you remember, for the sake of supporting your beliefs. Thus, if you’re an anti-immigration person, you would recall all the cases in which immigrants commit crimes, but not have such strong remembrance about the instances when American citizens commit the same crimes. Furthermore, you might even remember those select incidents rather differently from how they actually occurred.